P07640 - you type in 4 hrs to have a personal day off it creates a record of the default 8 hours

When I do a add from the P07640 (Leave Administration) I need to have 4 hrs for a personal day so I type in 4 hrs, it displays correctly and then when you click on Ok it takes you back to the leave adminsration program and you do a find it creates a record of 8 hrs where by you have to change it back to 4 hours and then it saves as 4 hrs. Please could you let me know how can I retain the 4 hours to the record generated...thank you