When one of the user's is trying to book a time off on the 31st of December, the time off screen shows that the requested days are '0' however in the same screen one day is taken off from the remaining balance.

More Information:
While trying to book a time off, the requested days off and the total remaining days that are displayed depending on various factors. To simplify this it can be explained in terms of a formula.

If we consider that the time off is being booked on the 31st of December, then the total balance as on the 31st of December can be calculated as the total number of hours accrued as on 31st of December minus all the past time off bookings minus all the time off bookings booked in the future till the closest future reset date.