diff --git a/quixstreams/dataframe/utils.py b/quixstreams/dataframe/utils.py
index b3cf9cba8..bb793afa4 100644
--- a/quixstreams/dataframe/utils.py
+++ b/quixstreams/dataframe/utils.py
@@ -1,4 +1,4 @@
-from datetime import timedelta
+from datetime import datetime, timedelta
 from typing import Union
 
 
@@ -22,3 +22,8 @@ def ensure_milliseconds(delta: Union[int, timedelta]) -> int:
             f'Timedelta must be either "int" representing milliseconds '
             f'or "datetime.timedelta", got "{type(delta)}"'
         )
+
+
+def now() -> int:
+    # TODO: Should be UTC time
+    return int(datetime.now().timestamp() * 1000)
diff --git a/quixstreams/dataframe/windows/base.py b/quixstreams/dataframe/windows/base.py
index 8040b2774..04d14de1b 100644
--- a/quixstreams/dataframe/windows/base.py
+++ b/quixstreams/dataframe/windows/base.py
@@ -17,7 +17,11 @@
 from typing_extensions import TypeAlias
 
 from quixstreams.context import message_context
-from quixstreams.core.stream import TransformExpandedCallback
+from quixstreams.core.stream import (
+    Stream,
+    TransformExpandedCallback,
+    TransformFunction,
+)
 from quixstreams.core.stream.exceptions import InvalidOperation
 from quixstreams.models.topics.manager import TopicManager
 from quixstreams.state import WindowedPartitionTransaction
@@ -42,6 +46,8 @@
     Iterable[Message],
 ]
 
+WallClockCallback = Callable[[WindowedPartitionTransaction], Iterable[Message]]
+
 
 class Window(abc.ABC):
     def __init__(
@@ -69,6 +75,13 @@ def process_window(
     ) -> tuple[Iterable[WindowKeyResult], Iterable[WindowKeyResult]]:
         pass
 
+    @abstractmethod
+    def process_wall_clock(
+        self,
+        transaction: WindowedPartitionTransaction,
+    ) -> Iterable[WindowKeyResult]:
+        pass
+
     def register_store(self) -> None:
         TopicManager.ensure_topics_copartitioned(*self._dataframe.topics)
         # Create a config for the changelog topic based on the underlying SDF topics
@@ -83,6 +96,7 @@ def _apply_window(
         self,
         func: TransformRecordCallbackExpandedWindowed,
         name: str,
+        wall_clock_func: WallClockCallback,
     ) -> "StreamingDataFrame":
         self.register_store()
 
@@ -92,12 +106,24 @@ def _apply_window(
             processing_context=self._dataframe.processing_context,
             store_name=name,
         )
+        wall_clock_transform_func = _as_wall_clock(
+            func=wall_clock_func,
+            stream_id=self._dataframe.stream_id,
+            processing_context=self._dataframe.processing_context,
+            store_name=name,
+        )
         # Manually modify the Stream and clone the source StreamingDataFrame
         # to avoid adding "transform" API to it.
         # Transform callbacks can modify record key and timestamp,
         # and it's prone to misuse.
-        stream = self._dataframe.stream.add_transform(func=windowed_func, expand=True)
-        return self._dataframe.__dataframe_clone__(stream=stream)
+        windowed_stream = self._dataframe.stream.add_transform(
+            func=windowed_func, expand=True
+        )
+        wall_clock_stream = Stream(
+            func=TransformFunction(wall_clock_transform_func, expand=True)
+        )
+        sdf = self._dataframe.__dataframe_clone__(stream=windowed_stream)
+        return sdf.concat_wall_clock(wall_clock_stream)
 
     def final(self) -> "StreamingDataFrame":
         """
@@ -140,9 +166,17 @@ def window_callback(
             for key, window in expired_windows:
                 yield (window, key, window["start"], None)
 
+        def wall_clock_callback(
+            transaction: WindowedPartitionTransaction,
+        ) -> Iterable[Message]:
+            # TODO: Check if this will work for sliding windows
+            for key, window in self.process_wall_clock(transaction):
+                yield (window, key, window["start"], None)
+
         return self._apply_window(
             func=window_callback,
             name=self._name,
+            wall_clock_func=wall_clock_callback,
         )
 
     def current(self) -> "StreamingDataFrame":
@@ -188,7 +222,17 @@ def window_callback(
             for key, window in updated_windows:
                 yield (window, key, window["start"], None)
 
-        return self._apply_window(func=window_callback, name=self._name)
+        def wall_clock_callback(
+            transaction: WindowedPartitionTransaction,
+        ) -> Iterable[Message]:
+            # TODO: Implement wall_clock callback
+            return []
+
+        return self._apply_window(
+            func=window_callback,
+            name=self._name,
+            wall_clock_func=wall_clock_callback,
+        )
 
     # Implemented by SingleAggregationWindowMixin and MultiAggregationWindowMixin
     # Single aggregation and multi aggregation windows store aggregations and collections
@@ -424,6 +468,28 @@ def wrapper(
     return wrapper
 
 
+def _as_wall_clock(
+    func: WallClockCallback,
+    processing_context: "ProcessingContext",
+    store_name: str,
+    stream_id: str,
+) -> TransformExpandedCallback:
+    @functools.wraps(func)
+    def wrapper(
+        value: Any, key: Any, timestamp: int, headers: Any
+    ) -> Iterable[Message]:
+        ctx = message_context()
+        transaction = cast(
+            WindowedPartitionTransaction,
+            processing_context.checkpoint.get_store_transaction(
+                stream_id=stream_id, partition=ctx.partition, store_name=store_name
+            ),
+        )
+        return func(transaction)
+
+    return wrapper
+
+
 class WindowOnLateCallback(Protocol):
     def __call__(
         self,
diff --git a/quixstreams/dataframe/windows/count_based.py b/quixstreams/dataframe/windows/count_based.py
index 57c6b36e5..973d23cce 100644
--- a/quixstreams/dataframe/windows/count_based.py
+++ b/quixstreams/dataframe/windows/count_based.py
@@ -189,6 +189,12 @@ def process_window(
         state.set(key=self.STATE_KEY, value=data)
         return updated_windows, expired_windows
 
+    def process_wall_clock(
+        self,
+        transaction: WindowedPartitionTransaction,
+    ) -> Iterable[WindowKeyResult]:
+        return []
+
     def _get_collection_start_id(self, window: CountWindowData) -> int:
         start_id = window.get("collection_start_id", _MISSING)
         if start_id is _MISSING:
diff --git a/quixstreams/dataframe/windows/time_based.py b/quixstreams/dataframe/windows/time_based.py
index c403cfdfa..4bfed4857 100644
--- a/quixstreams/dataframe/windows/time_based.py
+++ b/quixstreams/dataframe/windows/time_based.py
@@ -3,6 +3,7 @@
 from typing import TYPE_CHECKING, Any, Iterable, Literal, Optional
 
 from quixstreams.context import message_context
+from quixstreams.dataframe.utils import now
 from quixstreams.state import WindowedPartitionTransaction, WindowedState
 
 from .base import (
@@ -200,11 +201,23 @@ def process_window(
 
         return updated_windows, expired_windows
 
+    def process_wall_clock(
+        self,
+        transaction: WindowedPartitionTransaction,
+    ) -> Iterable[WindowKeyResult]:
+        return self.expire_by_partition(
+            transaction=transaction,
+            max_expired_end=now() - self._grace_ms,
+            collect=self.collect,
+            advance_last_expired_timestamp=False,
+        )
+
     def expire_by_partition(
         self,
         transaction: WindowedPartitionTransaction,
         max_expired_end: int,
         collect: bool,
+        advance_last_expired_timestamp: bool = True,
     ) -> Iterable[WindowKeyResult]:
         for (
             window_start,
@@ -214,6 +227,7 @@ def expire_by_partition(
             step_ms=self._step_ms if self._step_ms else self._duration_ms,
             collect=collect,
             delete=True,
+            advance_last_expired_timestamp=advance_last_expired_timestamp,
         ):
             yield key, self._results(aggregated, collected, window_start, window_end)
 
diff --git a/quixstreams/state/rocksdb/windowed/transaction.py b/quixstreams/state/rocksdb/windowed/transaction.py
index 3779b3e29..dfa3fa12a 100644
--- a/quixstreams/state/rocksdb/windowed/transaction.py
+++ b/quixstreams/state/rocksdb/windowed/transaction.py
@@ -298,6 +298,7 @@ def expire_all_windows(
         step_ms: int,
         delete: bool = True,
         collect: bool = False,
+        advance_last_expired_timestamp: bool = True,
     ) -> Iterable[ExpiredWindowDetail]:
         """
         Get all expired windows for all prefix from RocksDB up to the specified `max_end_time` timestamp.
@@ -360,9 +361,12 @@ def expire_all_windows(
                 if collect:
                     self.delete_from_collection(end=start, prefix=prefix)
 
-        self._set_timestamp(
-            prefix=b"", cache=self._last_expired_timestamps, timestamp_ms=last_expired
-        )
+        if advance_last_expired_timestamp:
+            self._set_timestamp(
+                prefix=b"",
+                cache=self._last_expired_timestamps,
+                timestamp_ms=last_expired,
+            )
 
     def delete_windows(
         self, max_start_time: int, delete_values: bool, prefix: bytes
diff --git a/quixstreams/state/types.py b/quixstreams/state/types.py
index c80c9e2ad..9f07b9499 100644
--- a/quixstreams/state/types.py
+++ b/quixstreams/state/types.py
@@ -378,6 +378,7 @@ def expire_all_windows(
         step_ms: int,
         delete: bool = True,
         collect: bool = False,
+        advance_last_expired_timestamp: bool = True,
     ) -> Iterable[ExpiredWindowDetail[V]]:
         """
         Get all expired windows for all prefix from RocksDB up to the specified `max_start_time` timestamp.
@@ -388,6 +389,7 @@ def expire_all_windows(
         :param max_end_time: The timestamp up to which windows are considered expired, inclusive.
         :param delete: If True, expired windows will be deleted.
         :param collect: If True, values will be collected into windows.
+        :param advance_last_expired_timestamp: If True, the last expired timestamp will be persisted.
         """
         ...