I dont want to be rude but... imagine yourself waiting for the burger in mc donalds about 30 minutes only because the cook is taking a sh#t.
You dont tell your costumer story like "GONNA DO IT LATER M8 IMA INSTALLING MAH TORENTOZ WYNDOUZ T10N". Just say "I need like 2 days to get my work done.. is it good for you?"
Lol, what is the problem with "I just gonna install my windows, after that I gonna start" .. You do not need to protect your friend, i know you two guys.