Most people run IGF 4-6 weeks (regardless of dosage) because of diminishing returns as your body gets used to it. I personally run it as long as I'm getting something out of it since I'm a high responder to IGF. I've run it longer than 8 weeks so if you're still getting good results near the end of 6 weeks, I'd keep going if it were me. The largest effect of IGF is usually fat loss. Depending on the dosage, there will be the creation of new muscle fibers in the applied muscle which in turn when they mature will cause a direct increase in muscle size. That part takes some time, and for obvious reasons works best when AAS is used at the same time.