Override hours in a working day, even with the working rota enabled

Currently, when the working rota enabled, the hours in a working day will be calculated automatically. 

If an employee works one half-day in a week, then this can skew all of the numbers by lowering the hours in a working day.

For example, if they normally work 7 hour days, but have one 3.5 hour day then the hours in a working day will end up less than 7, which means that full days will appear to consume 1.1 days allowance and half days will actually use 4.6 days.

What we would like is the ability to override the hours in a working day even with the working rota enabled.

This means that 7 hour days would consume exactly 1 day of allowance and half-days would consume exactly 0.5 days allowance