Thanks for your feedback! When I was making the game, I thought it took too long to get going, so I ended up making the spawn rate get 11% faster every round, starting at 4 seconds, when it used to be 3 seconds consistently, no matter how many dice. Though from what I have seen, people have had more difficulty with the game than I thought they would, so that means I didn't do great on difficulty balance. I also did add a bit of time for the dice to lock in, but since when it's on the ground, you usually cannot rotate it, it's only a third of a second. About the main theme, listening back on what I did, I think I made the second half too repetitive. I usually go for an "A B A C A B A D" song progression, but C in this case sounds too similar to B, so it sound like "A B A B A B A D", which is pretty repetitive.
Ah yeah, balancing in this short of time is always difficult. For the spawn rate and difficulty, it would also help to give the player some forewarning on when and where a new die will drop. Maybe some effect or pipe gearing up to drop some dice so the player can rush over underneath it or pop it off the ground before it gets locked.