diff --git a/aodntools/timeseries_products/hourly_timeseries.py b/aodntools/timeseries_products/hourly_timeseries.py
index 2e5be4e..66e5292 100644
--- a/aodntools/timeseries_products/hourly_timeseries.py
+++ b/aodntools/timeseries_products/hourly_timeseries.py
@@ -305,22 +305,22 @@ def PDresample_by_hour(df, function_dict, function_stats):
     :param df: pandas dataframe with ancillary variables and coords removed but with TIME as index
     :return: pandas dataframe
     """
-    ## back the index 30min
-    df.index = df.index - pd.Timedelta(30, units='m')
 
     varnames = df.columns
-    df_data = pd.DataFrame()
+    df_data = pd.DataFrame(index=pd.DatetimeIndex([]))
     for variable in varnames:
         ds_var = df[variable]
-        ds_var_mean = ds_var.resample('1H').apply(function_dict[variable]).astype(np.float32)
+        ds_var_resample = ds_var.resample('1H', base=0.5)  # shift by half hour to centre bin on the hour
+        ds_var_mean = ds_var_resample.apply(function_dict[variable]).astype(np.float32)
         df_data = pd.concat([df_data, ds_var_mean], axis=1, sort=False)
         for stat_method in function_stats:
-            ds_var_stat = ds_var.resample('1H').apply(stat_method).astype(np.float32)
+            ds_var_stat = ds_var_resample.apply(stat_method).astype(np.float32)
             ds_var_stat = ds_var_stat.rename("_".join([variable, stat_method]))
             df_data = pd.concat([df_data, ds_var_stat], axis=1, sort=False)
 
-    ##forward the index 30min
-    df_data.index = df_data.index + pd.Timedelta(30, units='m')
+    ##forward the index 30min so the timestamps are on the hour
+    df_data.index += pd.to_timedelta('30min')
+
     return df_data
 
 
diff --git a/test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220404.nc b/test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220428.nc
similarity index 58%
rename from test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220404.nc
rename to test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220428.nc
index d02738a..07d6952 100644
Binary files a/test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220404.nc and b/test_aodntools/timeseries_products/IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220428.nc differ
diff --git a/test_aodntools/timeseries_products/test_hourly_timeseries.py b/test_aodntools/timeseries_products/test_hourly_timeseries.py
index 3534494..07ad35b 100644
--- a/test_aodntools/timeseries_products/test_hourly_timeseries.py
+++ b/test_aodntools/timeseries_products/test_hourly_timeseries.py
@@ -21,7 +21,7 @@
 ]
 INPUT_PATHS = [os.path.join(TEST_ROOT, f) for f in INPUT_FILES]
 EXPECTED_OUTPUT_FILE = os.path.join(
-    TEST_ROOT, 'IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220404.nc'
+    TEST_ROOT, 'IMOS_ANMN-NRS_STZ_20181213_NRSROT_FV02_hourly-timeseries_END-20190523_C-20220428.nc'
 )
 
 INST_VARIABLES = {'instrument_id', 'source_file', 'LONGITUDE', 'LATITUDE', 'NOMINAL_DEPTH'}
@@ -89,6 +89,7 @@ def test_hourly_aggregator(self):
 
         # check variable values
         expected = Dataset(EXPECTED_OUTPUT_FILE)
+        self.assertEqual(len(expected['TIME']), len(dataset['TIME']))
         compare_vars = ('TIME', 'NOMINAL_DEPTH', 'instrument_index',
                         'TEMP', 'TEMP_count', 'TEMP_min', 'TEMP_max')
         non_match_vars = [var for var in compare_vars