Can't complete an IF statement, can you?

Hi there,

I'm usually ok with excel formulae but am really struggling here!!! Can anyone help me ??

I need a formula which will help me to use a spread sheet as a rota.

I have 16 staff and want to be able to enter their start times next to their finsh times i.e. 12:00 16:00 and have the formula work out how many hours this is, that is the easy bit. But I would like it to also work out the hours like this - if total shift time is between 4 hrs 15mins - 5hrs 45mins then minus 15mins from total shift time & if total shift time is more than 6hrs then minus 30mins from total shift time. I need this because our company do not pay for breaks, and if someone is able to get this to work for me I will be able to quickly work out our total number of ppaid hours per day and per week.

So please please help, my brains hurting

Thankyou