Does the enemy use logic when making moves or does it select a move at random? It seems fond of leaving its king in check when it has plenty of playable moves. Having to re-purchase pieces you sac is interesting, since in combination with the low value of mating the enemy king it incentivizes taking pieces before delivering mate, which in turn makes the clock more relevant. Nevertheless, I never felt I was under much time pressure in the current form. Game ends on level 11, which seemed like a good length. I would be concerned that even at that length you might hardlock the game if you don't lose enough material, though-- you get 2 pieces per round and start with only 15 available slots.
The enemy does indeed use logic when making moves, it just isn't very smart. The cost method that i used for its ai can defenetly have room for improvement.
I have had many opinions about the time needed to complete the game. It is a big difference between players with varying chess skills. In the future I would probably add a way to select diffulty levels and therefore I could decrease the time for more experienced players and increase the time for beginners.
Thank you for your supportive critique!