Having a single timeline to decide when cards are cast is a cool interpretation of the theme. Since shields drain over time, and you only see the next three moves of the enemy, I feel like there must be some kind of tricky strategy one could figure out to do well in the game. It definitely has potential.
I do wonder whether some kind of overall timeline indicator would make the game easier to understand, but at the same time, just placing a clock on the card and requiring the player to do mental arithmetic is part of the challenge.