We use PPLNS reward system. Our pool calculates the percentage of shares you send in the last 12000 shares for Ethash coins and 20000 for Equihash coins. Block reward is shared between miners proportionally to this percentage.
Depending on the pool hashrate it takes some time (usually couple of minutes) for the total amount of shares (12000 or 20000) to come up.
Therefore if you rig switches off a couple of seconds before the block was found - you would get you reward completely (as it was turned on). If it turns off 15 minutes before the block - you get nothing.