Hi Swetha,
It's not possible to declare a half day holiday.
Another option is that, you can modify the regular work plan as half day.
Go to Roster module
1) Create a regular day programme for the half working day
2) Go to regular work planner and select the location/department/employee. Then pick the option 'Clear the selected day' by double clicking on 24th December.Then save it.
3) Then on the same date assign the day programme you have created. Then save it.
4) Clear the Attendance data for the date and import again.
Regards,
Rincy