I don't believe so, although I'm not 100% sure.

Pretty sure you need a same "airport day" boarding pass. The new airport day is defined by the first flight out, usually something like 6 or 6:30am. I think they open security for that around 5am or so. (aka, you can obviously proceed through if you have a 1:30am flight...that's considered the same "day" as 11pm by the airport's counting). But if your flight is 8am or something, you must wait until 5am or whatever to go through.

Fyi, J class will be entirely irrelevant...it's not like J can get through and Y can't. Whatever is correct will hold true for all classes.

Last thought, just a heads up the CX lounges are not open 24 hours. In case that was part of the thinking. They kick folks out around 12 or 12:30am, with The Deck (CX lounge near gate 16, north side, near security) staying open until last flight around 2am. Then the lounges all close, until The Wing is the first to open, around 5am. The Wing opens downstairs first, and upstairs follows about 15-30 minutes later.