with me, it depends how neat i am.... if it's super neat with all the cables tie wrapped and everything aerodynamically good it's ~ 1 hour... messy as hell i can do it in 30 minutes... this is just a mobo, cpu, ram, 3 cards, floppy, cdrom and a HD..
my last build(not really a build just a case transfer) took me about 1:15 but that was a mobo, cpu, 3 sticks of ram, 5 cards, floppy, 2 cdroms, 4 case fans and a HD..