Since the release of this weeks update (r54964 USA_EU), the Reward for Daily Play never completes. It rewards fine (giving the 500 credits), but never actually completes. You can earn these credits again and again.
I have found that if you stay in the lobby after the completion of a game, and move automatically to the next map, you won’t get the Daily Play credit. But, if you exit lobby after completion of game, and immediately rejoin, you get the Daily Play credits again.