holiday time tracker

Hi,

Could someone please help me?
I have a group of employees that work 12 hour shifts over 3 days then have 2 days + weekends off. At some point they switch from mon - weds to weds - friday.

Some employees have 20 days holiday and some have more depending on the length of service.

If the employee is scheduled to work a bank holiday and they DO NOT work it then a deduction should be taken off their holiday allowance, but not a full day (4hours 48 mins).
If the employee is scheduled to work a bank holiday and they DO work it then 4 hours and 48 minutes should be added to their holiday allowance.

There are a number of other scenarios but i could figure them out if i can get the basics

Is there a way of excel counting 12 hours as 1 day and increasing the holiday allowance by 1 day if it reaches 12 and then reverting back to 0, or the remaining amount of hours and minutes

So for example if an employee has accrued 14 hours and 30 mins - it would equal 1 extra days holiday and 2 hours and 30 mins.

I have no layout so i am open to suggestions

I will need to list the holidays taken on the spreadsheet with dates taken and wether it is 1 day or just a number of hours etc.

TIA for your assistance.