Are you talking about running it as a cycle itself? Or are you using it for PCT?
If it's a cycle by itself to lose fat and retain muscle while cutting, then it can be used for as long as 8 weeks. After that your body gets used to it. (I was told this by AX rep C-los aka. MASSIVE.) Though I'm not sure if you really want to run it that long.
Maybe 4 weeks on, 4 weeks off...