From my experience, if you are not active in the game and in the area where you can choose days/endless levels, then you will not see the clock reset until you exit. For example, if you are in the store, the almanac, the Zen garden or playing a level when the clock hits 0:00, it will not be official until to you are back on the main screens (after hitting play on the app opening splash)
This has been the case for me for a long time. Also, if you are not connected to the internet, it might not reset your clock.
