How to define different pay rates based on the Day?

Hi,

We are facing the following case:

The workdays are from Monday to Friday. So if someone works on Saturdays needs to be paid with a different rate (1,25) and if he works on Sundays has to be paid with another one as well (1,50). Is there a way to define this rule so as the system to automatically recognise the Saturdays/Sundays and assign the specific rates (or pay types)?

Any idea would be very valuable for us.

Thanks

Lia