A pour would cost more in gas than it pays if it pushed a few cents to each of several hundred wallets. So at pour time the contract compares each wallet's share to the current cost of a transfer. Shares above that line are pushed. Shares below it are credited to the wallet's cup on that coin.
Cups are claimable any time on the cups page. A cup that is not claimed or added to for thirty days spills: its balance returns to the coin's pot and goes out with the next pour. The cups page shows a countdown to spill for every cup you have.