But that's already how bots are made. You don't need to add rules to the game before you can constrict the thinking time of entertainment AI

Challenging but fair bots are by definition not supposed to treat the game as totally algorithmically solvable. They can work fine on heuristics rather than algorithms, the same way that players do. There are moments when a player needs to think through all the possibilities available in the game state, and other moments when they just use a rule of thumb, like, "use this card to destroy the greatest threat currently out because time is not currently on my side to wait for what they might play next".