diff --git a/swc/aeon/io/api.py b/swc/aeon/io/api.py
index 3463058d..636f15e4 100644
--- a/swc/aeon/io/api.py
+++ b/swc/aeon/io/api.py
@@ -6,25 +6,52 @@
 from pathlib import Path
 
 import pandas as pd
+from typing_extensions import deprecated
 
-"""The duration of each acquisition chunk, in whole hours."""
 CHUNK_DURATION = 1
+"""The duration of each acquisition chunk, in whole hours."""
+
+REFERENCE_EPOCH = datetime.datetime(1904, 1, 1)
+"""The reference epoch for UTC harp time."""
 
 
+@deprecated("Please use the to_datetime function instead.")
 def aeon(seconds):
+    """Converts a Harp timestamp, in seconds, to a datetime object.
+
+    .. deprecated:: 0.2.0
+       This function is deprecated and will be removed in a future release.
+       Use :func:`to_datetime` instead.
+    """
+    return to_datetime(seconds)  # pragma: no cover
+
+
+def to_datetime(seconds):
     """Converts a Harp timestamp, in seconds, to a datetime object."""
-    return datetime.datetime(1904, 1, 1) + pd.to_timedelta(seconds, "s")
+    return REFERENCE_EPOCH + pd.to_timedelta(seconds, "s")
+
+
+def to_seconds(time):
+    """Converts a datetime object to a Harp timestamp, in seconds."""
+    if isinstance(time, pd.Series):
+        return (time - REFERENCE_EPOCH).dt.total_seconds()
+    else:
+        return (time - REFERENCE_EPOCH).total_seconds()
 
 
 def chunk(time):
     """Returns the whole hour acquisition chunk for a measurement timestamp.
 
-    :param datetime or Series time: An object or series specifying the measurement timestamps.
+    :param datetime, DatetimeIndex or Series time:
+        A datetime object, index or series specifying the measurement timestamps.
     :return: A datetime object or series specifying the acquisition chunk for the measurement timestamp.
     """
     if isinstance(time, pd.Series):
         hour = CHUNK_DURATION * (time.dt.hour // CHUNK_DURATION)
         return pd.to_datetime(time.dt.date) + pd.to_timedelta(hour, "h")
+    elif isinstance(time, pd.DatetimeIndex):
+        hour = CHUNK_DURATION * (time.hour // CHUNK_DURATION)
+        return pd.to_datetime(time.date) + pd.to_timedelta(hour, "h")
     else:
         hour = CHUNK_DURATION * (time.hour // CHUNK_DURATION)
         return pd.to_datetime(datetime.datetime.combine(time.date(), datetime.time(hour=hour)))
@@ -54,7 +81,7 @@ def chunk_key(file):
 
 def _set_index(data):
     if not isinstance(data.index, pd.DatetimeIndex):
-        data.index = aeon(data.index)
+        data.index = to_datetime(data.index)
     data.index.name = "time"
 
 
diff --git a/tests/io/test_api.py b/tests/io/test_api.py
index 1bed992c..15781deb 100644
--- a/tests/io/test_api.py
+++ b/tests/io/test_api.py
@@ -1,11 +1,14 @@
 """Tests for the aeon API."""
 
 from pathlib import Path
+from typing import cast
 
 import pandas as pd
 import pytest
+from pandas import testing as tm
 
 from swc import aeon
+from swc.aeon.io.api import chunk, to_datetime, to_seconds
 from tests.schema import exp02, social03
 
 monotonic_path = Path(__file__).parent.parent / "data" / "monotonic"
@@ -58,5 +61,43 @@ def test_pose_load_nonmonotonic_data_time_start_only_sort_fallback():
         assert data.index.is_monotonic_increasing
 
 
+@pytest.mark.parametrize(
+    "seconds",
+    [
+        0,  # Edge case: REFERENCE_EPOCH
+        123456789,  # Arbitrary value
+        pd.Series([0.0, 123456789.0]),  # Series value
+    ],
+)
+def test_datetime_seconds_conversion(seconds):
+    # test round-trip conversion
+    converted_datetime = to_datetime(seconds)
+    converted_seconds = to_seconds(converted_datetime)
+    if isinstance(seconds, pd.Series):
+        tm.assert_series_equal(converted_seconds, seconds)
+    else:
+        assert converted_seconds == seconds
+
+
+@pytest.mark.parametrize(
+    "time",
+    [
+        pd.Timestamp(0),  # Datetime value
+        pd.Series([pd.to_datetime(0)]),  # Series value
+        pd.DatetimeIndex([pd.to_datetime(0)]),  # Datetime index value
+    ],
+)
+def test_chunk_identity_conversion(time):
+    if isinstance(time, pd.Series):
+        time_chunk = cast(pd.Series, chunk(time))
+        tm.assert_series_equal(time_chunk, time)
+    elif isinstance(time, pd.DatetimeIndex):
+        time_chunk = cast(pd.DatetimeIndex, chunk(time))
+        tm.assert_index_equal(time_chunk, time)
+    else:
+        time_chunk = chunk(time)
+        assert time_chunk == time
+
+
 if __name__ == "__main__":
     pytest.main()