diff --git a/src/taskgraph/optimize/base.py b/src/taskgraph/optimize/base.py
index c6e84a5be..517c3e578 100644
--- a/src/taskgraph/optimize/base.py
+++ b/src/taskgraph/optimize/base.py
@@ -333,7 +333,7 @@ def replace_tasks(
         dependents = [target_task_graph.tasks[l] for l in dependents_of[label]]
         deadline = None
         if dependents:
-            now = datetime.datetime.utcnow()
+            now = datetime.datetime.now(datetime.timezone.utc)
             deadline = max(
                 resolve_timestamps(now, task.task["deadline"])
                 for task in dependents  # type: ignore
diff --git a/src/taskgraph/util/time.py b/src/taskgraph/util/time.py
index 6639e5ddd..a613f9e83 100644
--- a/src/taskgraph/util/time.py
+++ b/src/taskgraph/util/time.py
@@ -88,7 +88,7 @@ def json_time_from_now(input_str, now=None, datetime_format=False):
     """
 
     if now is None:
-        now = datetime.datetime.utcnow()
+        now = datetime.datetime.now(datetime.timezone.utc)
 
     time = now + value_of(input_str)
 
@@ -98,7 +98,7 @@ def json_time_from_now(input_str, now=None, datetime_format=False):
         # Sorta a big hack but the json schema validator for date does not like the
         # ISO dates until 'Z' (for timezone) is added...
         # Microseconds are excluded (see bug 1381801)
-        return time.isoformat(timespec="milliseconds") + "Z"
+        return time.replace(tzinfo=None).isoformat(timespec="milliseconds") + "Z"
 
 
 def current_json_time(datetime_format=False):
@@ -106,8 +106,9 @@ def current_json_time(datetime_format=False):
     :param boolean datetime_format: Set `True` to get a `datetime` output
     :returns: JSON string representation of the current time.
     """
+    now = datetime.datetime.now(datetime.timezone.utc)
     if datetime_format is True:
-        return datetime.datetime.utcnow()
+        return now
     else:
         # Microseconds are excluded (see bug 1381801)
-        return datetime.datetime.utcnow().isoformat(timespec="milliseconds") + "Z"
+        return now.replace(tzinfo=None).isoformat(timespec="milliseconds") + "Z"
diff --git a/test/test_optimize.py b/test/test_optimize.py
index 17a7b0ccb..af9924f7e 100644
--- a/test/test_optimize.py
+++ b/test/test_optimize.py
@@ -2,7 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from functools import partial
 
 import pytest
@@ -28,8 +28,10 @@ def should_remove_task(self, task, params, arg):
 
 class Replace(OptimizationStrategy):
     def should_replace_task(self, task, params, deadline, taskid):
-        expires = datetime.utcnow() + timedelta(days=1)
-        if deadline and expires < datetime.strptime(deadline, "%Y-%m-%dT%H:%M:%S.%fZ"):
+        expires = datetime.now(timezone.utc) + timedelta(days=1)
+        if deadline and expires.replace(tzinfo=None) < datetime.strptime(
+            deadline, "%Y-%m-%dT%H:%M:%S.%fZ"
+        ):
             return False
         return taskid
 
diff --git a/test/test_util_time.py b/test/test_util_time.py
index 8fd0e23ab..af9447f10 100755
--- a/test/test_util_time.py
+++ b/test/test_util_time.py
@@ -4,7 +4,7 @@
 
 
 import unittest
-from datetime import datetime
+from datetime import datetime, timezone
 from unittest.mock import patch
 
 from taskgraph.util.time import (
@@ -53,8 +53,13 @@ def test_json_from_now(self):
 
     def test_current_json_time(self):
         with patch("taskgraph.util.time.datetime.datetime") as mock_datetime:
-            mock_datetime.utcnow.return_value = datetime(2014, 1, 1)
+            mock_datetime.now.return_value = datetime(2014, 1, 1, tzinfo=timezone.utc)
             mock_datetime.side_effect = datetime
 
             assert current_json_time() == "2014-01-01T00:00:00.000Z"
-            assert current_json_time(True) == datetime(2014, 1, 1)
+            assert current_json_time(True) == datetime(2014, 1, 1, tzinfo=timezone.utc)
+
+    def test_json_from_now_tzinfo(self):
+        now = datetime(2014, 1, 1, tzinfo=timezone.utc)
+        self.assertEqual(json_time_from_now("1 years", now), "2015-01-01T00:00:00.000Z")
+        self.assertEqual(json_time_from_now("6 days", now), "2014-01-07T00:00:00.000Z")