If you don't feel the need to get it tonight, wait a little bit. Then when you do get it the servers wont be as backed up, and it should go faster. But iOS 5 is pretty sweet.
I tried when I got home at 8pm and had 0 errors and it couldn't have gone smoother. took less than an hour altogether and my iCloud and everything is setup and its great. iOS5 is a big upgrade over iOS4.