For me personally, length of time has had no impact on POIS symptoms only ejaculation has determined when symptoms are onset or not.
I've had no problem enjoying sex regularly and the only time i thought i had problems with sexual activity was when i was abstaining for long periods of time (to avoid POIS symptoms) then having sexual activity i would be overstimulated very fast and became a one poke joke lol. I was confused and anxious and depressed about this at the time not understanding myself but the answer became obvious later. Have sex/orgasms regularly and sensitivity is reduced, Have it less frequently and be hypersensitive and loose "stamina"
The downside for us obviously, is we feel better, symptom wise, without sex, so it's hard to maintain a regular sexual life. I am married now and I just focus on managing symptoms as I feel depriving my partner for too long is wrong and unfair. I have had intercourse before without ejaculating at the end and have felt fine/normal the next day. (No onset of POIS)