If you're using the Financial Management module, there is an option in the Rate Matrix to have a "standard rate" (i.e. your Contractor Daily Rate divided by 8) and an "overtime rate" (i.e. $0). That way when you view Actual hours/cost it will calculate based on the standard rate for 8 hours, then the overtime rate. Note we looked into this but never implemented it, so I'm not sure if it works as advertised. Note also that if you're using 7.5.x and you have a large number of resources (and/or projects), the Rate Matrix extract job can quickly become overloaded and take a long, looooong time to run!