I tested your game out. I found a bug: let's say you start a game and want to quit it before you finish. When you start a new game juste after, the time is reset, but the current progress is kept. With that being said I managed to get a highscore under 5 seconds...
There also seems to be a bit of mess with the activities of your game. You never actually seem to terminate them, and they keep on pilling up when you change your game's screens. Maybe take a look at the .finish() method of the activity class to better manage that. I got crashes likely related to that issue, I reported them so you should get complete data in your Developers console.
A part from those small issues, the concept is very fun and original I thought! Keep up with the work!