From What I've read, it is better to run fina for between 6 & 12 weeks at least. I've heard of people running it a lot longer, taking the correct precautions of course, & not having any sides from it. I'm currently running an 8 week w/ test, dbol, & eq. But like Canuck said it depends on what your goals, stats, & dosage are.
If it were me & i was running 750 mg. of sust per week, I'd be running the fina the entire duratin of the cycle at 75 mg. ed or 150 eod. Make sure you've got your antis on hand bro.