Time in gym needed for coins?

Speculation says an hour, have yet to have a pokemon return though

1 hour, and rounded down.

One coin per hour. Less than a hour, no coin

Not sure yet, but it seems like one coin per hour.

I got into 3 gyms before getting home yesterday and the mons came back with 8 ~ 10 coins today after I woke up. If I'm correct, the coins matches the hours they defended the gyms.

Just got my Donphan returned to me after 14 hours. Got 14 coins in return.

Am I missing something? I have had 2 defenders return, one after 2+ hours and one after 12+ hours. But my coin account has not moved at all. My gym defender badge is all I have to show for the two. Do I need to do anything to get coins released?