single drop box with machine numbers selectible then a drop with diff time choices to

I am tryin to help the Maintenence Corrdinator here at our company with a lil problem, I have attached a copy of what we use right now to keep up with daily work orders on machines But im tryin to figure out a way to have a single drop box with machine numbers selectible then a drop with diff time choices to choose from and have excel auto sum the daily down time ofr the week and the entire month automatically. Any help would be great and Thank you.