I stayed on for (I can't remember exactly) between 9-12 months a few years ago (not ideal I know) and I tapered off using a SERM (I tapered off after a 12 week cycle with no SERM and my recovery was worse than a 9-12 month cycle with taper and a SERM) and it took me a good 9 months to feel fully recovered and I actually stayed off for just over 12 months. I didn't have blood work done, which is obviously the 'acid test' so I always gauged my recovery by my libido.
I remember prisoner saying in his thread that the six weeks on 100mg a week can be counted as time off, and the additional tapering down weeks, the 90,80,70.,60,60mg... per weeks until off are also obviously counted as weeks off.
I also came off after 9 months with only a SERM pct, which was similarly successful to the taper (I came off quickly due to skin problems) so from experience I believe that, at least for me the SERM aspect of the taper is very important. I personally wouldn't consider a taper necessary for a 3 month cycle, Westclock laid out his own PCT recently which is well worth reading.
How long do you plan staying on for before coming 'off' using the taper?
In answer to your question though time off is as long as it takes you to recover properly, this is down to the individual and the choice of steroids used (at least for me-and I've never used Deca) So to gauge this properly as BBB says you need to have blood work done.
It takes great self discipline to keep coming off and staying off, I think its also down to the individuals capacity to recover (if you recover t production fully every time you come 'off' being off won't be a problem, but take the word of a HRT patient, if you feel your PCT hasn't been 100% effective, DO NOT think 'fuck it' and go back on, unless you plan on NEEDING to stay back on PERMANENTLY.
I would go as far to say that some peoples endocrine systems are just tougher than others so PCT is simply more effective on some people than others, but there's only one way to find out...