You can always replay a previous passed stage, this is useful when there is a particular item you need in that stage.

After you shoot enough hearts in a stage, you can exit the stage by tapping the exit icon, without waiting for the time.

After you shoot enough hearts in a stage, you get EXP points for extra hearts shoot.

If you run out of arrows and there is no arrows in current stage, the game will be finished, whatever time up or not.