diff --git a/src/post_processing/dataclass/data_aplose.py b/src/post_processing/dataclass/data_aplose.py
index 0939966..59cb01b 100644
--- a/src/post_processing/dataclass/data_aplose.py
+++ b/src/post_processing/dataclass/data_aplose.py
@@ -167,7 +167,21 @@ def __getitem__(self, item: int) -> Series:
         return self.df.iloc[item]
 
     def change_tz(self, tz: str | tzinfo) -> None:
-        """Change the timezone of the DataFrame and of the begin and end Timestamps."""
+        """Change the timezone of a DataAplose instance.
+
+        Examples
+        --------
+        >>> import pytz
+        >>> data = DataAplose(...)
+        >>> data.change_tz(pytz.timezone("Etc/GMT-2"))
+
+        >>> data = DataAplose(...)
+        >>> data.change_tz("UTC")
+
+        >>> data = DataAplose(...)
+        >>> data.change_tz("UTC+02:00")
+
+        """
         self.df["start_datetime"] = [
             elem.tz_convert(tz)
             for elem in self.df["start_datetime"]
diff --git a/src/post_processing/utils/filtering_utils.py b/src/post_processing/utils/filtering_utils.py
index db1484f..5083c7d 100644
--- a/src/post_processing/utils/filtering_utils.py
+++ b/src/post_processing/utils/filtering_utils.py
@@ -6,6 +6,7 @@
 import csv
 from typing import TYPE_CHECKING
 
+import pytz
 from pandas import (
     DataFrame,
     Timedelta,
@@ -19,8 +20,6 @@
 if TYPE_CHECKING:
     from pathlib import Path
 
-    from dateutil.tz import tzoffset
-
     from post_processing.dataclass.detection_filter import DetectionFilter
 
 
@@ -176,9 +175,18 @@ def get_dataset(df: DataFrame) -> list[str]:
     return datasets if len(datasets) > 1 else datasets[0]
 
 
-def get_timezone(df: DataFrame) -> tzoffset | list[tzoffset]:
+def get_timezone(df: DataFrame):
     """Return timezone(s) from DataFrame."""
-    timezones = {ts.tz for ts in df["start_datetime"] if ts.tz is not None}
+
+    def get_canonical_tz(tz):
+        if hasattr(tz, "zone") and tz.zone:
+            return pytz.timezone(tz.zone)
+        if hasattr(tz, "key"):
+            return pytz.timezone(tz.key)
+        return pytz.UTC
+
+    timezones = {get_canonical_tz(ts.tzinfo) for ts in df["start_datetime"]}
+
     if len(timezones) == 1:
         return next(iter(timezones))
     return list(timezones)
diff --git a/tests/test_filtering_utils.py b/tests/test_filtering_utils.py
index f8a3745..622ad2a 100644
--- a/tests/test_filtering_utils.py
+++ b/tests/test_filtering_utils.py
@@ -1,8 +1,8 @@
 import csv
-from datetime import timezone
 from pathlib import Path
 
 import pytest
+import pytz
 from pandas import DataFrame, Timedelta, Timestamp, date_range
 
 from post_processing.utils.filtering_utils import (
@@ -170,10 +170,10 @@ def test_get_dataset(sample_df: DataFrame) -> None:
 
 def test_get_timezone_single(sample_df: DataFrame) -> None:
     tz = get_timezone(sample_df)
-    assert isinstance(tz, timezone)
+    assert tz == pytz.utc
 
-# %% read DataFrame
 
+# %% read DataFrame
 
 def test_read_dataframe_comma_delimiter(tmp_path: Path) -> None:
     csv_file = tmp_path / "test.csv"