the rule of thumb is time on (including pct) = time off. of course it all depends on your goals...but this method is thought of as fairly safe.

i generally take equal or greater period of time off then on .........that said however i have taken as short as 4 weeks off providing my bloodwork is good.....its important to realize that you need time off for your nerves and connective tissue to play catchup...
its not exactly natural for your body to put on 20lbs in 3 months and you do need time off to adjust....

Here's my view on this:
1. If you're looking to return you HPTA completely to "normal" you'll need at least time on = time off.
2. If you're looking to return your HPTA mostly to normal while generally giving your body a break from the cycle you'll need time on = 1/2 time off.