You could take it for as long as you like. Just treat it like any other anabolic with regards to PCT. I've done multiple 2, 3 and 4 weekers with it. Personally, I liked the 3 week cycles the most. Good gains with very little suppression. A sound, general rule of thumb is to double your off weeks before going back on. IE: 3 weeks on, 6 weeks off, repeat. A little conservative but works very well. Altough, if you have 6 weeks worth try what I did last year and make outstanding gains:
3 months total. 2 weeks on (1 ser. Mag10/day)followed by 2 weeks off (Alpha Male/M combo). Repeat for a total of three cycles.