diff --git a/src/quartz_api/internal/backends/test_utils.py b/src/quartz_api/internal/backends/test_utils.py
new file mode 100644
index 00000000..c7525c15
--- /dev/null
+++ b/src/quartz_api/internal/backends/test_utils.py
@@ -0,0 +1,20 @@
+import datetime as dt
+import unittest
+
+from .utils import get_window
+
+
+class TestGetWindow(unittest.TestCase):
+    def test_get_window_with_reference_time(self) -> None:
+        reference_time = dt.datetime(2024, 1, 10, 15, 30, tzinfo=dt.UTC)
+
+        start, end = get_window(reference_time=reference_time)
+
+        self.assertEqual(
+            start,
+            dt.datetime(2024, 1, 8, 0, 0, tzinfo=dt.UTC),
+        )
+        self.assertEqual(
+            end,
+            dt.datetime(2024, 1, 12, 0, 0, tzinfo=dt.UTC),
+        )
diff --git a/src/quartz_api/internal/backends/utils.py b/src/quartz_api/internal/backends/utils.py
index 98ec4566..9fa00254 100644
--- a/src/quartz_api/internal/backends/utils.py
+++ b/src/quartz_api/internal/backends/utils.py
@@ -3,17 +3,27 @@
 import datetime as dt
 
 
-def get_window() -> tuple[dt.datetime, dt.datetime]:
-    """Returns the start and end of the window for timeseries data."""
+def get_window(
+    reference_time: dt.datetime | None = None,
+) -> tuple[dt.datetime, dt.datetime]:
+    """Returns the start and end of the window for timeseries data.
+
+    Args:
+        reference_time: The time to base the window on. If None, defaults to now (UTC).
+    """
+    if reference_time is None:
+        reference_time = dt.datetime.now(tz=dt.UTC)
+
     # Window start is the beginning of the day two days ago
-    start = (dt.datetime.now(tz=dt.UTC) - dt.timedelta(days=2)).replace(
+    start = (reference_time - dt.timedelta(days=2)).replace(
         hour=0,
         minute=0,
         second=0,
         microsecond=0,
     )
+
     # Window end is the beginning of the day two days ahead
-    end = (dt.datetime.now(tz=dt.UTC) + dt.timedelta(days=2)).replace(
+    end = (reference_time + dt.timedelta(days=2)).replace(
         hour=0,
         minute=0,
         second=0,