diff --git a/gallery_dl/extractor/common.py b/gallery_dl/extractor/common.py
index 48b9ca7b..ff49d893 100644
--- a/gallery_dl/extractor/common.py
+++ b/gallery_dl/extractor/common.py
@@ -183,7 +183,7 @@ class Extractor():
         elif until:
             if isinstance(until, datetime.datetime):
                 # convert to UTC timestamp
-                until = (until - util.EPOCH) / util.SECOND
+                until = util.datetime_to_timestamp(until)
             else:
                 until = float(until)
             seconds = until - now
diff --git a/gallery_dl/formatter.py b/gallery_dl/formatter.py
index da79213b..27d5e40e 100644
--- a/gallery_dl/formatter.py
+++ b/gallery_dl/formatter.py
@@ -254,7 +254,7 @@ def parse_format_spec(format_spec, conversion):
             "C": string.capwords,
             "j": json.dumps,
             "t": str.strip,
-            "T": util.to_timestamp,
+            "T": util.datetime_to_timestamp_string,
             "d": text.parse_timestamp,
             "U": text.unescape,
             "S": util.to_string,
diff --git a/gallery_dl/util.py b/gallery_dl/util.py
index a5aa5eb2..7d1cc32d 100644
--- a/gallery_dl/util.py
+++ b/gallery_dl/util.py
@@ -173,8 +173,13 @@ def to_string(value):
     return str(value)
 
 
-def to_timestamp(dt):
-    """Convert naive datetime to UTC timestamp string"""
+def datetime_to_timestamp(dt):
+    """Convert naive UTC datetime to timestamp"""
+    return (dt - EPOCH) / SECOND
+
+
+def datetime_to_timestamp_string(dt):
+    """Convert naive UTC datetime to timestamp string"""
     try:
         return str((dt - EPOCH) // SECOND)
     except Exception:
diff --git a/test/test_util.py b/test/test_util.py
index 9b0045c8..d5b9784f 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -537,7 +537,16 @@ class TestOther(unittest.TestCase):
         self.assertEqual(f(["a", "b", "c"]), "a, b, c")
         self.assertEqual(f([1, 2, 3]), "1, 2, 3")
 
-    def test_to_timestamp(self, f=util.to_timestamp):
+    def test_datetime_to_timestamp(self, f=util.datetime_to_timestamp):
+        self.assertEqual(f(util.EPOCH), 0.0)
+        self.assertEqual(f(datetime.datetime(2010, 1, 1)), 1262304000.0)
+        self.assertEqual(f(datetime.datetime(2010, 1, 1, 0, 0, 0, 128000)),
+                         1262304000.128000)
+        with self.assertRaises(TypeError):
+            f(None)
+
+    def test_datetime_to_timestamp_string(
+            self, f=util.datetime_to_timestamp_string):
         self.assertEqual(f(util.EPOCH), "0")
         self.assertEqual(f(datetime.datetime(2010, 1, 1)), "1262304000")
         self.assertEqual(f(None), "")