Which airport are you referring to? This is a thread for YVR and YYZ

I'm gonna make assumptions that it's YVR and you're flying either domestically (due to citing the 8pm PPL closure) or on BR9 (just a hunch)

If domestically, you can check in at any time, not at the airline's suggested time, and then head on over to the PPL or the MLL and enjoy it if you wish.

If internationally, the PPL on the international side should close shortly before BR9 departs, the website lists a 12:30AM closure now. If you really need a shower, pop by the MLL before AC7 departs for the evening since it should be emptier (you'll have access as a BR*G or BR J pax)

You say that check-in time is 9:45PM, and while that's probably true, I've noticed a massive, massive, massive queue in front of the check-in desk before the agents actually show up, so you might want to get in line a bit before that time to skip the line if you're checking bags