I would've liked more interactions or challenges (x number of cards you can use, different math operations...). I understand where you were going, it just lacks "juicyness". Watch this talk by Martin Jonasson and Petri Purho, I try to apply it to every game I do: 

Well, how can I begin. What I liked most was the background, it's looking great. But I couldn't figure out what was the point of the gameplay, I mean, I realized we had to use the buttons to always put the number in between the min and max, but I felt it's not appealing enough to be the main gameplay of the game. Maybe if we had a few more math related mechanics or a context happening in between those "Bath times" the game could be feel another way.