Congrats! This is good fun to play and a good, simple 20-second game. I don't have any problems with the execution except maybe that the easy mode could be a bit easier and that the stamped, red text at the end of the game is distorted and hard to make out.
If I *had* to suggest improvements for a v2, I would think about ways to make it just a little deeper. Maybe some simple way to engage the player's thinking beyond the timing skill requirement. A few boxes with different dimensions or shapes might do it.