i commented on x's page regarding this. many people will flame me, but honestly start my pct depending on how much im taking of something and what its ha;f life is. if you run 500 mg a week of prop, and start your pct four days after you last injection and then on your next cycle you decide to run 1,000 a week of prop (not recommended, just using an example) your pct should start at least twice as long as your first pct timing. when i feel like my pct hasn't quite done the job, i just extend my aromosin out however long i feel is appropriate.