The current default behavior when filtering a field with fieldType of date is that the time is set to the beginning of the day. So if the user filters by greater than (after) a date, they still see that day's rows included. The default behavior for operators > and <= should be that the time is set to end of day.

We currently do this in the FilterChooserFieldSpec's valueParser in Admin/Activity's tracking and client error tabs. The tracking tab also has column filters enabled, so if the user were to filter by > a timestamp, for example, they would see different results depending on whether they used the column filter or filter chooser.