I think keeping the same time limit for all courses is unrealistic. The time required for the final levels of each campaign in particular seem grossly inadequate.
Some of the activities that become more difficult over time can be really frustrating. When catching snails it's often impossible to reach the next one once they're moving moderately quickly, seals can pop up and back down in half a second, and the math questions get really difficult quickly. Maybe something could be done to offset things like this: maybe add the ability to upgrade how quickly the bucket moves in snail catching; something similar for whacking seals, and perhaps the amount of time allotted for multiplication could be related to its difficulty (it seems strange to get six seconds to do both 3*2 and, say, 44*38). But definitely a really fun game nonetheless - I can't get enough!
Finally finished all 40 levels without using any hints! It's a mark of good conception and development when a game that's actually pretty short can keep you occupied (and frustrated!) for days on end... really excellent game!
congrats on that