diff --git a/HISTORY.rst b/HISTORY.rst
index 0fb1246..5ea67bd 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -8,7 +8,8 @@ History
 ------------------
 * **breaking changes**
 
-    * none yet
+    * :class:`Resource` class: replace :meth:`last_request_at()` with :meth:`last_request_age_s()`
+      (e.g see :meth:`tickets.Ticket.last_request_age_s()`)
 
 * **added features**
 
@@ -22,7 +23,7 @@ History
 ------------------
 * **breaking changes**
 
-    * none yet
+    * none
 
 * **added features**
 
diff --git a/tests/test_cache.py b/tests/test_cache.py
index 2aeb5d7..9942273 100644
--- a/tests/test_cache.py
+++ b/tests/test_cache.py
@@ -157,17 +157,16 @@ def test_clear():
     assert not cache
 
 
-def test_timestamp():
+def test_age_s():
     import time
     from datetime import datetime, timezone
 
     cache = LruCache()
-    assert cache.timestamp("foo") is None
+    assert cache.age_s("foo") is None
+
     cache["foo"] = "bar"
-    timestamp = cache.timestamp("foo")
-    assert isinstance(timestamp, datetime)
-    assert timestamp.tzinfo == timezone.utc
 
-    time.sleep(0.01)
+    time.sleep(0.015)
+    assert cache.age_s("foo") > 0.015
     cache["foo"] = "baz"
-    assert cache.timestamp("foo") > timestamp
+    assert cache.age_s("foo") < 0.015
diff --git a/tests/test_tickets.py b/tests/test_tickets.py
index 2f734db..3769a3f 100644
--- a/tests/test_tickets.py
+++ b/tests/test_tickets.py
@@ -180,10 +180,8 @@ def test_ticket_create_article_sender_and_type_attribute(single_ticket):
 
 
 def test_ticket_last_request_at(single_ticket):
-    from datetime import datetime
-
-    timestamp = single_ticket.last_request_at()
-    assert isinstance(timestamp, datetime)
+    age_s = single_ticket.last_request_age_s()
+    assert isinstance(age_s, float)
 
 
 def test_lazy_attribute_caching(caplog, rclient):
diff --git a/zammadoo/cache.py b/zammadoo/cache.py
index 4cc78bb..8623bee 100644
--- a/zammadoo/cache.py
+++ b/zammadoo/cache.py
@@ -2,14 +2,11 @@
 # -*- coding: UTF-8 -*-
 from collections import OrderedDict
 from collections.abc import Hashable
-from datetime import datetime, timedelta, timezone
 from time import monotonic
 from typing import Generic, Optional, Tuple, TypeVar
 
 _T = TypeVar("_T")
 
-_START_OFFSET = datetime.now(timezone.utc) - timedelta(seconds=monotonic())
-
 
 class LruCache(Generic[_T]):
     def __init__(self, max_size: int = -1) -> None:
@@ -93,9 +90,8 @@ def __setitem__(self, item: Hashable, value: _T) -> None:
     def __delitem__(self, item: Hashable) -> None:
         del self._cache[item]
 
-    def timestamp(self, item: Hashable) -> Optional[datetime]:
-        ts_sec = self._cache.get(item, (None, None))[0]
-        if ts_sec:
-            return _START_OFFSET + timedelta(seconds=ts_sec)
-
-        return None
+    def age_s(self, item: Hashable) -> Optional[float]:
+        try:
+            return monotonic() - self._cache[item][0]
+        except KeyError:
+            return None
diff --git a/zammadoo/resource.py b/zammadoo/resource.py
index a4935bb..03e1a4d 100644
--- a/zammadoo/resource.py
+++ b/zammadoo/resource.py
@@ -1,7 +1,6 @@
 #!/usr/bin/env python
 # -*- coding: UTF-8 -*-
 
-from datetime import datetime
 from typing import TYPE_CHECKING, Any, List, Optional, Tuple
 
 from .resources import ResourcesT
@@ -93,9 +92,9 @@ def reload(self, expand=False) -> None:
         )
         info.update(new_info)
 
-    def last_request_at(self) -> Optional[datetime]:
-        """:return: the last request timestamp"""
-        return self.parent.cache.timestamp(self.url)
+    def last_request_age_s(self) -> Optional[float]:
+        """:return: time in seconds since the last request"""
+        return self.parent.cache.age_s(self.url)
 
 
 class UserProperty(_AttributeBase):