Overtime Hours Calculation

Hi All,

I am struggling with my formulas to work out overtime hours based on a start time and finish time versus core hours.

The rules that i need to apply using a formula is as follows -

1 - Any work done before 9am
2 - Any work done after 5:30pm
3 - Any weekend work

Start and Finish times can be at any time during the 24 hour clock, cross over the core time and also any duration.

Where i am falling down is where the start time is 22:30 and finish time is 00:00 (i.e. midnight) - this should be 1:30 of overtime and also where i have instances of a start time of 03:00 and finish time of 07:00 which should be caluclated as 4 hours of overtime.

If anybody can help that would be much appreciated.

Thanks.
Pritesh...