I figured it was something like that but the trouble is you end up thinking someone's there and then when they don't message you back you think they're ignoring you..... don't suppose there's an easy answer to this.
I can safely say, most people are usually tucked up in bed at 3am - and if they're known to you and you/them, they will reply anyway. But think - 3am is quite early and most won't be active due to work etc that morning?
Although I do know a lot are active deep into the night too.
Well there is an easy answer to it. Message someone if you are trying to get hold of them, and if they're there - they will reply.
If not, they won't until later on, if at all.
I doubt many will be around at 3am though..