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.
These Emoji fraction activities are perfect for a math center, whole group / early finisher assignment or even homework! Students will have a blast while reducing and simplifying, comparing and ordering, adding and subtracting, identifying simple fractions as decimals and converting improper and mixed fractions.