Do you know software that can help me calculate finish date (with time) given a start date and duration?

I need it for making a simple production schedule. example: the start date is 31 August 2009 10.00 AM and the duration of the work is 63 hours. I need a software that can calculate the finish date. with the attention that there are 8 hours work from monday-friday, 5 hours in the saturday, and [...]