Primo is active for two weeks. So let's day you're taking a shot EOD, that means you've reached the peak amount within the second week. You may not see RESULTS until much later though and people mistaken think that;s because it was somehow "dormant" all that time.
Personally I see results after a week. Then again, I know what I'm doing. I train naturally for the most part and I have a lot of muscle memory. If all you've ever done is rely on steroids for gains, then yeah, you won't notice anything for a while, especially with something like Primo because it's subtle, slow and steady. But the muscle is solid.