The Super Famicom Box plays a sound and displays the current available time on top of the currently running game or in the top right corner in the menu.
Purchased game time is kept by the system even when changing games or turning the device off. And is only deducted during game play* (Menu use is free of charge)
*game play = the time the game itself runs, even if it's the title screen or a cutscene.
If the timer has 5 seconds left, the Super Famicom box displays a countdown and halts the game when it reaches zero. The user can then exit the game, or purchase more time to resume the game where it was.
After the coin box has been set up in the options menu, every detected coin adds the specified amount of time (0-99 minutes).