If you're using an Access Date/Time field for this value, the format
of the field is *absolutely irrelevant*.

Date/Time values are stored internally as a Double Float number, a
count of days and fractions of a day (times) since midnight, December
30, 1899. The format of the field is *not* part of the stored value;
it merely controls how the number is displayed.

Try setting the format of the field in the table to Long Time (don't
worry, this won't change the contents of any field). Are any of the
values off by a second or so? A field might contain the actual numeric
value 0.5625 which would *display* as 01:30pm, or as 13:30, or as
#12/30/1899 13:30:00# or any of a variety of other appearances;
another record might contain 0.562511574074074 (one second later),
which would DISPLAY as 13:30 (since forcing the hh:nn format will
truncate the remaining second) but not be equal. A Long Time would
show it as 13:30:01.

Depending on how the data was entered into the field, you might even
have two values which differ by less than a half-second; since Access
doesn't have provision for sub-second display accuracy, these values
could be different yet look the same.

                 John W. Vinson[MVP]