I've only ever captured one gym and I got 10 pokécoins immediately and another 10 and 500 stardust after 21 hours. Anyone know how the payout sytem works?
You get 10 Pokécoins and 500 Stardust for each Gym you are currently, at the point of retrieval, holding. This only works up to 10 Gyms for a total of 100 Pokécoins and 5000 Stardust.
You can retrieve every 21 hours as long as you have a Pokémon in at least 1 Gym.
Therefore it is an efficient tactic to gather as many Gyms as possible in a small timeframe, and at the point you hold the most - retrieve your rewards.