Very cute use of the theme (it's always good to see the countdown used as a mechanic and not simply a time limit). I like the playfulness of the puzzles: some countdowns are helpful, others not, and some can be reused throughout the puzzles.
One feedback I would give is that it's a bit presumptive (condescending even?) to show the hint for the level on screen at all times. I want to figure it out myself first. Props for coming up with a hint on each puzzle, but let me ask for it.
Also it would be good if the puzzles were "tighter". Many of them can be solved by swapping haphazardly and not having to come up with a solid solution. In particular, most puzzles have redundant counters that you don't need to use at all (which means you can take your pick of any counters) - it would feel neater if every counter was either needed, or was an obstacle to be avoided (i.e. it should be the case that removing any counter from a puzzle would make it impossible, or make it trivial).