Yep, when I go, I normally I aim to get to my seat just before the teams come out, Maybe a quick toilet stop, possibly a coffee, if I'm really early (like 20 minutes early)Mate, there won’t be 40 fans in the stadium an hour before kick off, never mind 40k. That’s not how we do it in England.
Years ago, when I wasn't old enough to drink (drinking being an absolutely integral part of my 80s and 90s matchday experience for obvious reasons ) I spent many a boring hour watching teams going through their warm ups, even ,at away grounds coming out to 'inspect the pitch' in their suits (as they used to wear) when they arrive!! I used to wonder if the game would ever start!!
Having said the above, when the game actually starts I do try to get involved, clap, cheer, sing (if you call it that) express my views (sometimes quite colourfully!)
as much as I can.
Also, I have only left early once at COMS/Etihad, that was that astoundingly dreadful game against Forest in the FA Cup, where with about 15 mins to go I simply couldn't take anymore!!!