timesheet formula

Hi

Could you please help me with a formula for my timesheets?

I have attached part of a timesheet but I don't know how to work out times for all the day and night shift workers in 24 hour clock (which is what we have to use) and splitting the time into ordinary time and anything after midnight on Friday is time and a half and also Sunday to Monday.

e.g. start time 1900 - finish time 0730 is 12.5 hours ordinary time

Friday 1900 - 0730 into Saturday would be 5 hours ordinary time and 7.5 time and a half
Sunday 1900 - 0730 into Monday would be 7.5 hours ordinary time and 5 hours time and a half

Thanks very much