I didn't remember the exact dates, so I consulted my notebook. The shortest break I had between 6wk solo cycles was ~7wks (more like 6wks and 2 days to be exact). This was somewhat irresponsible on my part and is not something I would recommend to everyone. Although I was getting blood work done routinely, so I kind of knew where I was hormone wise and made the informed decision to run two cycles with minimal time off in between.
In general I would recommend a longer time off between cycles, and in my opinion it is totally feasible for you to safely run 2 7wk osta cycles in a year. You would be on for 14 wks out of a year, that leaves 38 weeks you are off, which equates to almost 20 weeks off between cycles, more than enough for you to recover.
If you wanted to push the envelope even three 7wk cycles a year is not out of the question, that would be 21 wks on, 31 wks off, so 10 wks between each cycle, but I would wait to see how you respond to osta and the results you get before considering this option.
Also, if you can keep a personal journal or notebook of your entire cycle; dates you start, dosing amounts/dosing time everyday, time off, everything else you are taking and results you see in gym and on the scale, it is an invaluable tool for measuring your progress and objectively evaluating how your body responds to a compound.
*Edit* I forgot to ask, how much nolva do you plan on using? You might not need it, but its good that you have it.