I agree with everyone who says that it's not about when you play, but how much you play that really matters. I know people who are in bed by 9 PM because that’s just their routine, and I know others who only start playing at that time and keep going until morning. That only
tells you whether someone’s a night owl or not — nothing more.
What actually says something about a player’s potential problems is how much time they spend playing. But even that can be misleading, because if you’re playing long tournaments, it’s normal for them to last hours.
So maybe the best indicator of a problem is how much someone loses in a single day. That’s the real signal. Like, if you’re playing, you bust out of a tournament after hours, and then you register for another one just to keep going... yeah, that’s when you’ve probably got a problem.
That’s how I see it, anyway.