Standard answer is time off should be equal to or greater than time on, so in your case at least 10 weeks. But like raj said, make sure your bloods look good. If they got seriously out of whack it would probably be a good idea to wait longer. You should have seen this somewhere in your reading, but if you were doing a ton of reading it's possible it got lost in the shuffle or you just missed it.
Nolva is just for PCT, and 20mg/day is sufficient for the entire PCT - no real reason to do 40 the first week or two. Read 'PCT dosing on this forum is wrong'.
Also, don't forget an AI while on - arimidex, exemestane, etc. Arimidex is the standard for most guys, I've always used exemestane (aromasin) since it does a better job of preventing E backlash at the end.