I have done this before
I haven’t camp right on one but have stayed in an area close and as soon as I saw my Pokémon return notification was back at the Gym within minutes. Didn’t care if the person was still there or not.
2 can play the knock out strait away game .
I once spent an hour at 1 gym Because red team kept golden raspberry and taking it right back so I stayed there for an hour taken from them they eventually gave up and went home
Do that often. Fight over a gym for an hour. They usually do feed the whole gym so that is kind of an attack on their reserves. I always have to throw out revives if I don’t have battles like this. I enjoy the idea that somewhere someone is boiling and throwing stuff through the room. Even if they don’t. I like the idea. That totally makes my day AWESOME.
I rarely battle because I do not really like it and once the owners of the Gym start Berrying, I move on to somewhere else. That’s why I rather just go to yellow Gyms that still have a place for me left.
I will sit and wait as long as it takes