S4 generally kicks in pretty fast. I start noticing effects within a few days, similar to when running any oral AAS. It has a short half life, so many will recommend a split dosing per day. I always dose just once per day in the morning. Technically once you reach peak levels of the compound, you don't need to dose as often since you will always have a continuous supply in your blood. It doesn't hurt to dose twice per day, but I don't think its absolutely necessary