ms access general date format problems

hi there..... i am creating an access database for a schedule of employees work times..... i am using a general date format to calculate the number of hours worked..... but when i try to input data entry as 29/5/03 12:00:00 am on a certain day it just displays a null value..... but if i put 29/5/03 12:00:01 am it works fine.... is there any way to get around this.....

thanx in advance