diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 1d4dff57f..0ca58e988 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -4,6 +4,8 @@ Changelog
 Next
 ----
 
+- Add ``sleep_fn`` parameter to ``MockVWS`` for injecting a custom delay strategy, enabling deterministic and fast tests without monkey-patching.
+
 2026.02.15.3
 ------------
 
diff --git a/src/mock_vws/_requests_mock_server/decorators.py b/src/mock_vws/_requests_mock_server/decorators.py
index 08f63f982..411cc3298 100644
--- a/src/mock_vws/_requests_mock_server/decorators.py
+++ b/src/mock_vws/_requests_mock_server/decorators.py
@@ -70,6 +70,7 @@ def __init__(
         target_tracking_rater: TargetTrackingRater = _BRISQUE_TRACKING_RATER,
         real_http: bool = False,
         response_delay_seconds: float = 0.0,
+        sleep_fn: Callable[[float], None] = time.sleep,
     ) -> None:
         """Route requests to Vuforia's Web Service APIs to fakes of those
         APIs.
@@ -91,6 +92,10 @@ def __init__(
             target_tracking_rater: A callable for rating targets for tracking.
             response_delay_seconds: The number of seconds to delay each
                 response by. This can be used to test timeout handling.
+            sleep_fn: The function to use for sleeping during response
+                delays. Defaults to ``time.sleep``. Inject a custom
+                function to control virtual time in tests without
+                monkey-patching.
 
         Raises:
             MissingSchemeError: There is no scheme in a given URL.
@@ -98,6 +103,7 @@ def __init__(
         super().__init__()
         self._real_http = real_http
         self._response_delay_seconds = response_delay_seconds
+        self._sleep_fn = sleep_fn
         self._mock: RequestsMock
         self._target_manager = TargetManager()
 
@@ -136,6 +142,7 @@ def add_database(self, database: VuforiaDatabase) -> None:
     def _wrap_callback(
         callback: _Callback,
         delay_seconds: float,
+        sleep_fn: Callable[[float], None],
     ) -> _Callback:
         """Wrap a callback to add a response delay."""
 
@@ -159,11 +166,11 @@ def wrapped(
                 effective = float(timeout)
 
             if effective is not None and delay_seconds > effective:
-                time.sleep(effective)
+                sleep_fn(effective)
                 raise requests.exceptions.Timeout
 
             result = callback(request)
-            time.sleep(delay_seconds)
+            sleep_fn(delay_seconds)
             return result
 
         return wrapped
@@ -195,6 +202,7 @@ def __enter__(self) -> Self:
                         callback=self._wrap_callback(
                             callback=original_callback,
                             delay_seconds=self._response_delay_seconds,
+                            sleep_fn=self._sleep_fn,
                         ),
                         content_type=None,
                     )
diff --git a/tests/mock_vws/test_requests_mock_usage.py b/tests/mock_vws/test_requests_mock_usage.py
index 46e22112d..4b9cf1f5c 100644
--- a/tests/mock_vws/test_requests_mock_usage.py
+++ b/tests/mock_vws/test_requests_mock_usage.py
@@ -195,6 +195,54 @@ def test_delay_with_tuple_timeout() -> None:
                 timeout=(5.0, 0.1),
             )
 
+    @staticmethod
+    def test_custom_sleep_fn_called_on_delay() -> None:
+        """
+        When a custom ``sleep_fn`` is provided, it is called instead of
+        ``time.sleep`` for the non-timeout delay path.
+        """
+        calls: list[float] = []
+        with MockVWS(
+            response_delay_seconds=5.0,
+            sleep_fn=calls.append,
+        ):
+            requests.get(
+                url="https://vws.vuforia.com/summary",
+                headers={
+                    "Date": rfc_1123_date(),
+                    "Authorization": "bad_auth_token",
+                },
+                data=b"",
+                timeout=30,
+            )
+        assert calls == [5.0]
+
+    @staticmethod
+    def test_custom_sleep_fn_called_on_timeout() -> None:
+        """
+        When a custom ``sleep_fn`` is provided, it is called instead of
+        ``time.sleep`` for the timeout path.
+        """
+        calls: list[float] = []
+        with (
+            MockVWS(
+                response_delay_seconds=5.0,
+                sleep_fn=calls.append,
+            ),
+            pytest.raises(expected_exception=requests.exceptions.Timeout),
+        ):
+            requests.get(
+                url="https://vws.vuforia.com/summary",
+                headers={
+                    "Date": rfc_1123_date(),
+                    "Authorization": "bad_auth_token",
+                },
+                data=b"",
+                timeout=1.0,
+            )
+        # sleep_fn should have been called with the effective timeout
+        assert calls == [1.0]
+
 
 class TestProcessingTime:
     """Tests for the time taken to process targets in the mock."""