There are a few quick and dirty rules for deloading, or taking a planned lay-off.
The first one is one that Dan John and I have discussed until we were sick of the topic, and it's basically every 4th week you need to either significantly lighten the load, not train at all, or do some sort of significantly different, yet not-very-taxing activity
(I am invoking Dan John's name here like he's my own personal savior and to add authority to my statements....heh)
You can dabble with that length of time, at some points in my training lifetime, I would go 8-10 weeks hard, or 5-6 weeks hard. Very dependent on your training and nutritional status. The heavy 1RM stuff that powerlifters and olympic lifters live on is really the major stuff that needs cycling.
The second is more counter-intuitive.
If you hit a PR, pack it up, do some abs, go on home. Take a day or two off.
Why? A PR, especially for a guy like me who's been lifting a long time, is a significant event. A breakthrough. And it is also something that now needs to be recovered from. You've done something you've never done before.
Although, when I am talking about these kinds of PRs, I am talking about PRs in long-practiced lifts, not in a lift that's new to your training regimen. A good example of this would be the guy who's struggled with reaching a 500# squat...when he hits it, it's a significant personal milestone, both mentally and physically.