Cute idea... good way to get them to learn square roots without them knowing it because they know the numbers under the post its! It is very inexpensive and not at all time consuming to make. The only problem I can think of with this would be the postit notes loosing their ability to stick onto the clock's face.
Squares and Roots Bingo! Great way for middle school math students to practice their squares and square roots! Comes with 30 game boards and calling cards. The game can be used as a whole group, small group math centers, or for math intervention.
Math to the 7th Power: Inverse Operations GameInverse Operations Game This is a game I call Name that Operation. I use it to help the students build on prior knowledge of inverse operations and then use that to understand the connection between squares and square roots, cubes and cube roots and then later in the year, distributive property and factoring. Here are some slides I use in class to play the game: