diff --git a/cyclops/data/slicer.py b/cyclops/data/slicer.py
index 92e74563a..f0282bd1c 100644
--- a/cyclops/data/slicer.py
+++ b/cyclops/data/slicer.py
@@ -768,7 +768,7 @@ def _apply_mask(
         months = pc.month(example_values)
         mask = _apply_mask(months, month, mask)
     if day is not None:
-        days = pc.year(example_values)
+        days = pc.day(example_values)
         mask = _apply_mask(days, day, mask)
     if hour is not None:
         hours = pc.hour(example_values)
diff --git a/docs/source/tutorials/nihcxr/monitor_api.ipynb b/docs/source/tutorials/nihcxr/monitor_api.ipynb
index 53e9ebcd3..b6662ddda 100644
--- a/docs/source/tutorials/nihcxr/monitor_api.ipynb
+++ b/docs/source/tutorials/nihcxr/monitor_api.ipynb
@@ -25,7 +25,6 @@
    "source": [
     "\"\"\"NIHCXR Clinical Drift Experiments Tutorial.\"\"\"\n",
     "\n",
-    "\n",
     "import random\n",
     "\n",
     "import numpy as np\n",
diff --git a/tests/cyclops/data/test_slicer_datetime.py b/tests/cyclops/data/test_slicer_datetime.py
new file mode 100644
index 000000000..6ed07fd5f
--- /dev/null
+++ b/tests/cyclops/data/test_slicer_datetime.py
@@ -0,0 +1,14 @@
+"""Focused datetime slicing tests."""
+
+import pyarrow as pa
+
+from cyclops.data.slicer import filter_datetime
+
+
+def test_filter_datetime_matches_day_of_month() -> None:
+    """Test filtering datetimes by day-of-month."""
+    table = pa.table({"dt": ["2020-01-07", "2020-01-14", "2021-01-07"]})
+
+    result = filter_datetime(table, column_name="dt", day=7)
+
+    assert result == [True, False, True]