I was thinking of doing something very similar to this, set up a way for the game to track how many minutes has passed by checking the timer variable i have now and then as the mins go up have it add a certain amount to the enemy mob speed, then an amount to health and damage or other things as well; I havent fully fleshed it out but this is the same track i was feeling so i appreciate the feedback to see others are thinking along the same lines as I have been