hmmmm
it will not provide you the value by simple minus formula, you need some editing also....
1. right click on columns of start time and end time. and go to format cells - click on time - from the list select the suitable format as per requirement .. e.g. 1:30:55 PM
2. Now select the total hours column and go to format cells again - click on custom (last option in the drop down list) - from the list select h: mm: ss .
3. in total hours column use the formula ... (End time - start time)
4. it will give you the total login/working hours..
5. after getting working hours, you may substract Total working hours from regular hours and it will give you overtime hours.. but make sure all cells are formatted to time format h: mm: ss
use this formula
=IF(F23<E23,E23-F23,"no overtime")