Sorry, no. Project does not understand concepts of X amount of square footage per day. I understands Work, Duration, and Assignment units. By you telling Project Work, it will calculate Duration based upon the Work and the resource assignment units. 1 resource working 8 hours per day can accomplish 40 hours of work in 5 days. 1 resource working 6 hours per day can accomplish 40 hours of work in 6.67 days.