Pokemon Go gym etiquette? (I’m new)

I just started playing Pokemon Go so I could play with my brother’s kids and I know very little.

I took over my first gym and then was wracked with guilt picturing small children crying their eyes out over their pokemon, so I started googling to see what the consensus was on player etiquette.

From what I understand, as long as a pokemon has been in a gym for 8.5 hours the owner will get the full 5o coins for the day. But I also keep seeing something about the coin reset at 12:01 and read that you shouldn’t take a gym between 11 pm and midnight and I really do not get it. Can someone enlighten me? I did see there had been changes to the game over the years so maybe the stuff I’m reading is not all up-to-date.