diff --git a/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py b/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
index 1757a117..39782327 100644
--- a/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
+++ b/rosbridge_library/src/rosbridge_library/capabilities/defragmentation.py
@@ -1,5 +1,5 @@
 import threading
-from datetime import datetime
+import time
 
 from rosbridge_library.capability import Capability
 
@@ -84,13 +84,13 @@ def __init__(self, protocol):
     #   4.b) pass the reconstructed message string to protocol.incoming()       # protocol.incoming is checking message fields by itself, so no need to do this before passing the reconstructed message to protocol
     #   4.c) remove the fragment list to free up memory
     def defragment(self, message):
-        now = datetime.now()
+        now = time.monotonic()
 
         if self.received_fragments is not None:
             for id in self.received_fragments.keys():
                 time_diff = now - self.received_fragments[id]["timestamp_last_append"]
                 if (
-                    time_diff.total_seconds() > self.fragment_timeout
+                    time_diff > self.fragment_timeout
                     and not self.received_fragments[id]["is_reconstructing"]
                 ):
                     log_msg = ["fragment list ", str(id), " timed out.."]
@@ -188,7 +188,7 @@ def defragment(self, message):
             log_msg = "".join(log_msg)
             self.protocol.log("debug", log_msg)
 
-            duration = datetime.now() - now
+            duration = time.monotonic() - now
 
             # Pass the reconstructed message to rosbridge
             self.protocol.incoming(reconstructed_msg)
@@ -196,7 +196,7 @@ def defragment(self, message):
             log_msg.extend([str(msg_total), " fragments. "])
             # cannot access msg.data if message is a service_response or else!
             # log_msg += "[message length: " + str(len(str(json.loads(reconstructed_msg)["msg"]["data"]))) +"]"
-            log_msg.extend(["[duration: ", str(duration.total_seconds()), " s]"])
+            log_msg.extend(["[duration: ", str(duration), " s]"])
             log_msg = "".join(log_msg)
             self.protocol.log("info", log_msg)
 
diff --git a/rosbridge_library/src/rosbridge_library/internal/subscription_modifiers.py b/rosbridge_library/src/rosbridge_library/internal/subscription_modifiers.py
index e68faee4..ac129c5c 100644
--- a/rosbridge_library/src/rosbridge_library/internal/subscription_modifiers.py
+++ b/rosbridge_library/src/rosbridge_library/internal/subscription_modifiers.py
@@ -31,10 +31,10 @@
 # POSSIBILITY OF SUCH DAMAGE.
 
 import sys
+import time
 import traceback
 from collections import deque
 from threading import Condition, Thread
-from time import time
 
 """ Sits between incoming messages from a subscription, and the outgoing
 publish method.  Provides throttling / buffering capabilities.
@@ -66,10 +66,10 @@ def set_queue_length(self, queue_length):
         return self.transition()
 
     def time_remaining(self):
-        return max((self.last_publish + self.throttle_rate) - time(), 0)
+        return max((self.last_publish + self.throttle_rate) - time.monotonic(), 0)
 
     def handle_message(self, msg):
-        self.last_publish = time()
+        self.last_publish = time.monotonic()
         self.publish(msg)
 
     def transition(self):
diff --git a/rosbridge_library/test/internal/subscribers/test_subscription_modifiers.py b/rosbridge_library/test/internal/subscribers/test_subscription_modifiers.py
index 27d149b8..597961df 100755
--- a/rosbridge_library/test/internal/subscribers/test_subscription_modifiers.py
+++ b/rosbridge_library/test/internal/subscribers/test_subscription_modifiers.py
@@ -146,9 +146,9 @@ def cb(msg):
         handler.publish = cb
 
         self.assertTrue(handler.time_remaining() == 0)
-        t1 = time.time()
+        t1 = time.monotonic()
         handler.handle_message(msg)
-        t2 = time.time()
+        t2 = time.monotonic()
 
         self.assertEqual(received["msg"], msg)
         self.assertLessEqual(t1, handler.last_publish)