I’ve definitely used multiple lounges at Changi after arriving with long layovers, where I’ve arrived early morning, used the lounge to relax/freshen up, then go into city, then came back multiple hours later before boarding an evening flight. What I can’t remember is which BP I used to enter. I want to think it is my arriving one, because not sure about SIN specifically, but most lounges here in US won’t let you even enter until 3 hours prior to your flight. I do remember going into SATS this spring at SIN after arrival on a TR redeye, and again, don’t remember which BP I showed, but definitely was told I could only stay for 3 hours - we left before then (I don’t know about others - while it’s nice to have access to a lounge for a little while, mostly don’t want to stay for multiple hours on end anyway…). I don’t know for sure if/how they planned to monitor that and if I would have been asked to leave then.