diff --git a/testing/Cycles.h b/testing/Cycles.h
new file mode 100644
index 00000000..93633c5e
--- /dev/null
+++ b/testing/Cycles.h
@@ -0,0 +1,29 @@
+/* -*- mode: c++ -*-
+ * Copyright (C) 2020  Keyboard.io, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+namespace kaleidoscope {
+namespace testing {
+
+struct Cycles {
+  uint32_t value;
+};
+
+}  // namespace testing
+}  // namespace kaleidoscope
diff --git a/testing/ExpectedKeyboardReport.cpp b/testing/ExpectedKeyboardReport.cpp
index 152a5af5..ad4e3508 100644
--- a/testing/ExpectedKeyboardReport.cpp
+++ b/testing/ExpectedKeyboardReport.cpp
@@ -31,7 +31,7 @@ const std::set<uint8_t> & ExpectedKeyboardReport::Keycodes() const {
   return keycodes_;
 }
 
-uint32_t ExpectedKeyboardReport::Timestamp() const {
+Millis ExpectedKeyboardReport::Timestamp() const {
   return timestamp_;
 }
 
diff --git a/testing/ExpectedKeyboardReport.h b/testing/ExpectedKeyboardReport.h
index 85ef298c..a87cfb20 100644
--- a/testing/ExpectedKeyboardReport.h
+++ b/testing/ExpectedKeyboardReport.h
@@ -21,23 +21,25 @@
 #include <set>
 #include <string>
 
+#include "testing/Millis.h"
+
 namespace kaleidoscope {
 namespace testing {
 
 class ExpectedKeyboardReport {
  public:
-  ExpectedKeyboardReport(uint32_t timestamp,
+  ExpectedKeyboardReport(Millis timestamp,
                          const std::set<uint8_t> & keycodes,
                          std::string message = "");
 
   const std::set<uint8_t> & Keycodes() const;
 
-  uint32_t Timestamp() const;
+  Millis Timestamp() const;
 
   const std::string & Message() const;
 
  private:
-  uint32_t timestamp_;
+  Millis timestamp_;
   std::set<uint8_t> keycodes_;
   std::string failure_message_;
 };
diff --git a/testing/Millis.h b/testing/Millis.h
new file mode 100644
index 00000000..77fc7b0f
--- /dev/null
+++ b/testing/Millis.h
@@ -0,0 +1,111 @@
+/* -*- mode: c++ -*-
+ * Copyright (C) 2020  Keyboard.io, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+namespace kaleidoscope {
+namespace testing {
+
+struct Millis {
+  uint32_t value;
+
+  constexpr bool operator==(const Millis& other) const {
+    return this->value == other.value;
+  }
+  constexpr bool operator!=(const Millis& other) const {
+    return !(*this == other);
+  }
+  constexpr bool operator<(const Millis& other) const {
+    return this->value < other.value;
+  }
+  constexpr bool operator>(const Millis& other) const {
+    return this->value > other.value;
+  }
+  constexpr bool operator<=(const Millis& other) const {
+    return this->value <= other.value;
+  }
+  constexpr bool operator>=(const Millis& other) const {
+    return this->value >= other.value;
+  }
+
+  Millis operator+(const Millis& other) {
+    return Millis{this->value + other.value};
+  }
+  Millis operator-(const Millis& other) {
+    return Millis{this->value - other.value};
+  }
+  Millis operator+(const uint32_t raw) {
+    return Millis{this->value + raw};
+  }
+  Millis operator-(const uint32_t raw) {
+    return Millis{this->value - raw};
+  }
+
+  Millis& operator=(const uint32_t raw) {
+    this->value = raw;
+    return *this;
+  }
+  Millis& operator+=(const uint32_t raw) {
+    this->value += raw;
+    return *this;
+  }
+  Millis& operator-=(const uint32_t raw) {
+    this->value -= raw;
+    return *this;
+  }
+
+  constexpr bool operator<(uint32_t raw) const {
+    return this->value < raw;
+  }
+  constexpr bool operator>(uint32_t raw) const {
+    return this->value > raw;
+  }
+  constexpr bool operator<=(uint32_t raw) const {
+    return this->value <= raw;
+  }
+  constexpr bool operator>=(uint32_t raw) const {
+    return this->value >= raw;
+  }
+
+  operator size_t() {
+     return value;
+  }
+};
+
+constexpr bool operator<(uint32_t x, const Millis& y) {
+  return x < y.value;
+}
+constexpr bool operator>(uint32_t x, const Millis& y) {
+  return x > y.value;
+}
+constexpr bool operator<=(uint32_t x, const Millis& y) {
+  return x <= y.value;
+}
+constexpr bool operator>=(uint32_t x, const Millis& y) {
+  return x >= y.value;
+}
+
+constexpr Millis operator+(uint32_t x, const Millis& y) {
+  return Millis{x + y.value};
+}
+constexpr Millis operator-(uint32_t x, const Millis& y) {
+  return Millis{x - y.value};
+}
+
+}  // namespace testing
+}  // namespace kaleidoscope
diff --git a/testing/VirtualDeviceTest.cpp b/testing/VirtualDeviceTest.cpp
index 80d3a0d4..59b9ad92 100644
--- a/testing/VirtualDeviceTest.cpp
+++ b/testing/VirtualDeviceTest.cpp
@@ -31,6 +31,24 @@ std::unique_ptr<State> VirtualDeviceTest::RunCycle() {
   return State::Snapshot();
 }
 
+// =============================================================================
+void VirtualDeviceTest::Run(Cycles n) {
+  sim_.RunCycles(n.value);
+}
+
+void VirtualDeviceTest::Run(Millis t) {
+  sim_.RunForMillis(t);
+}
+
+void VirtualDeviceTest::RunUntil(Millis end) {
+  uint32_t t0 = Runtime.millisAtCycleStart();
+  Run(Millis{end - t0});
+}
+
+void VirtualDeviceTest::RunFrom(Millis start, Millis t) {
+  RunUntil(Millis{start + t});
+}
+
 // =============================================================================
 void VirtualDeviceTest::LoadState() {
   output_state_ = State::Snapshot();
@@ -47,24 +65,44 @@ const HIDState* VirtualDeviceTest::HIDReports() const {
   return output_state_->HIDReports();
 }
 
-uint32_t VirtualDeviceTest::ReportTimestamp(size_t index) const {
+Millis VirtualDeviceTest::ReportTimestamp(size_t index) const {
   uint32_t t = output_state_->HIDReports()->Keyboard(index).Timestamp();
-  return t;
+  return Millis{t};
 }
 
 // -----------------------------------------------------------------------------
-uint32_t VirtualDeviceTest::EventTimestamp(size_t index) const {
-  return input_timestamps_[index];
+Millis VirtualDeviceTest::EventTimestamp(size_t index) const {
+  return Millis{input_timestamps_[index]};
 }
 
 // =============================================================================
 void VirtualDeviceTest::PressKey(KeyAddr addr) {
   sim_.Press(addr);
-  input_timestamps_.push_back(Runtime.millisAtCycleStart());
+  input_timestamps_.push_back(Millis{Runtime.millisAtCycleStart()});
 }
 void VirtualDeviceTest::ReleaseKey(KeyAddr addr) {
   sim_.Release(addr);
-  input_timestamps_.push_back(Runtime.millisAtCycleStart());
+  input_timestamps_.push_back(Millis{Runtime.millisAtCycleStart()});
+}
+
+// -----------------------------------------------------------------------------
+void VirtualDeviceTest::PressKey(Cycles n, KeyAddr addr) {
+  sim_.RunCycles(n.value);
+  PressKey(addr);
+}
+void VirtualDeviceTest::ReleaseKey(Cycles n, KeyAddr addr) {
+  sim_.RunCycles(n.value);
+  ReleaseKey(addr);
+}
+
+// -----------------------------------------------------------------------------
+void VirtualDeviceTest::PressKey(Millis t, KeyAddr addr) {
+  sim_.RunForMillis(t);
+  PressKey(addr);
+}
+void VirtualDeviceTest::ReleaseKey(Millis t, KeyAddr addr) {
+  sim_.RunForMillis(t);
+  ReleaseKey(addr);
 }
 
 
@@ -86,7 +124,7 @@ void VirtualDeviceTest::ExpectReport(Keycodes keys,
 void VirtualDeviceTest::ExpectReport(AddKeycodes added_keys,
                                      RemoveKeycodes removed_keys,
                                      std::string description) {
-  uint32_t report_timestamp = Runtime.millisAtCycleStart();
+  Millis report_timestamp{Runtime.millisAtCycleStart()};
   for (Key key : added_keys) {
     AddToReport(key);
   }
@@ -109,6 +147,34 @@ void VirtualDeviceTest::ExpectReport(RemoveKeycodes removed_keys,
   ExpectReport(AddKeycodes{}, removed_keys, description);
 }
 
+// -----------------------------------------------------------------------------
+void VirtualDeviceTest::ExpectReport(Cycles n,
+                                     AddKeycodes added_keys,
+                                     std::string description) {
+  sim_.RunCycles(n.value);
+  ExpectReport(added_keys, description);
+}
+void VirtualDeviceTest::ExpectReport(Cycles n,
+                                     RemoveKeycodes removed_keys,
+                                     std::string description) {
+  sim_.RunCycles(n.value);
+  ExpectReport(removed_keys, description);
+}
+
+// -----------------------------------------------------------------------------
+void VirtualDeviceTest::ExpectReport(Millis t,
+                                     AddKeycodes added_keys,
+                                     std::string description) {
+  sim_.RunForMillis(t);
+  ExpectReport(added_keys, description);
+}
+void VirtualDeviceTest::ExpectReport(Millis t,
+                                     RemoveKeycodes removed_keys,
+                                     std::string description) {
+  sim_.RunForMillis(t);
+  ExpectReport(removed_keys, description);
+}
+
 // =============================================================================
 void VirtualDeviceTest::ClearReport() {
   current_keyboard_keycodes_.clear();
diff --git a/testing/VirtualDeviceTest.h b/testing/VirtualDeviceTest.h
index d2c17620..b5c61ba1 100644
--- a/testing/VirtualDeviceTest.h
+++ b/testing/VirtualDeviceTest.h
@@ -18,6 +18,8 @@
 
 #include <cstddef>
 
+#include "testing/Cycles.h"
+#include "testing/Millis.h"
 #include "testing/ExpectedKeyboardReport.h"
 #include "testing/SimHarness.h"
 #include "testing/State.h"
@@ -59,6 +61,24 @@ class VirtualDeviceTest : public ::testing::Test {
 
   SimHarness sim_;
 
+  // ---------------------------------------------------------------------------
+  // Utility functions to advance time in the simulator.
+
+  // Run the simulator `n` cycles
+  void Run(Cycles n);
+
+  // Run the simulator `t` (virtual) milliseconds
+  void Run(Millis t);
+
+  // Run the simulator until the (virtual) clock reaches `end` milliseconds
+  void RunUntil(Millis end);
+
+  // Run the simulator until the (virtual) clock advances `t` milliseconds past
+  // `start`. This is most useful when testing timeouts based on an input event
+  // that is not the most recent one (e.g. a timeout following a keypress, but
+  // with a key release in between).
+  void RunFrom(Millis start, Millis t);
+
   // ---------------------------------------------------------------------------
   // A representation of the set of observed HID reports accumulated by the
   // simulator as a testcase executes. It starts out empty, and a call to
@@ -79,21 +99,28 @@ class VirtualDeviceTest : public ::testing::Test {
   const HIDState* HIDReports() const;
 
   // Get the timestamp of a logged Keyboard HID report
-  uint32_t ReportTimestamp(size_t index) const;
+  Millis ReportTimestamp(size_t index) const;
 
   // ---------------------------------------------------------------------------
   // A vector of timestamps for input events. Calls to `PressKey()` &
   // `ReleaseKey()` append timestamps to it when called.
-  std::vector<uint32_t> input_timestamps_ = {};
+  std::vector<Millis> input_timestamps_ = {};
 
   // Get the timestamp of a logged input event from `output_state_`
-  uint32_t EventTimestamp(size_t index) const;
+  Millis EventTimestamp(size_t index) const;
 
   // ---------------------------------------------------------------------------
   // Press/release a keyswitch & log the input event timestamp
   void PressKey(KeyAddr addr);
   void ReleaseKey(KeyAddr addr);
 
+  // Run for `n` cycles, then press/release a keyswitch
+  void PressKey(Cycles n, KeyAddr addr);
+  void ReleaseKey(Cycles n, KeyAddr addr);
+
+  // Run for `t` milliseconds, then press/release a keyswitch
+  void PressKey(Millis t, KeyAddr addr);
+  void ReleaseKey(Millis t, KeyAddr addr);
 
   // ---------------------------------------------------------------------------
   // The following functions all add an expected value of HID report to the
@@ -112,6 +139,12 @@ class VirtualDeviceTest : public ::testing::Test {
   void ExpectReport(AddKeycodes added_keys, std::string description);
   void ExpectReport(RemoveKeycodes removed_keys, std::string description);
 
+  void ExpectReport(Cycles n, AddKeycodes added_keys, std::string description);
+  void ExpectReport(Cycles n, RemoveKeycodes removed_keys, std::string description);
+
+  void ExpectReport(Millis t, AddKeycodes added_keys, std::string description);
+  void ExpectReport(Millis t, RemoveKeycodes removed_keys, std::string description);
+
   // ---------------------------------------------------------------------------
   std::set<uint8_t> current_keyboard_keycodes_ = {};
   // Manage the set of keycodes expected in the next report