SARMs stay in the system for as long as you’re taking them, of course. It takes SARMs between 48-72 hours to kick in for most people and once it does, the SARMs stay in effect for the duration of the cycle that you’re on. They’re potent supplements that are designed to be used to help someone build a lot of muscle: it takes a little while for them to leave the system.
Even after you finish your SARMs cycle, that doesn’t mean that the effects of SARMs are over. Instead what happens is you’ll likely need to take PCT just to make sure that you don’t have any negative long-term hormonal effects from taking the SARMs. Otherwise, it’ll take a long time for your testosterone to stop being suppressed, and during that time, you’ll have to deal with a wide list of unfun, dangerous side effects. It’s not recommended to be in that state for any longer than absolutely necessary.
Once your PCT is complete and your body has recovered, it’s say to safe that the SARMs are gone by then.