No, the Changi Lounge is is both a departures and arrivals lounge. It is landside and explicitly is for arrivals as well. Their Priority Pass contract says that you must have a valid boarding pass for same-day travel and can enter up to four hours before departure. They should just say that you must enter the lounge within four hours of landing as well, and do away with the same-day boarding pass requirement. If you land between midnight and 11 PM, you can use the lounge for sure. If you arrive between 11 PM and 11:40 PM in Terminal 1, you can still probably use the lounge. If you arrive after 11 PM in other Terminals you probably can't. That's absurd.

The lounge dragons are extremely punctilious. I arrived once, out of breath, at 12:10 AM, having landed in another terminal at 11:30 with checked baggage and I was denied entry. I was told to take it up with Priority Pass. I called Priority Pass, spoke to an agent, and they were not helpful at all.