How did you do the timer for each level? Why can't you use the same method for 10 levels?
You can create a global variable StartTime, set it to time on start of level 1, and add this event:
Compare global variable StartTime<(time-6000) -> (game over)
The problem with using global variable is that you'll have to adjust its value when player pauses the game.
Or you can start a timer for 6000 seconds on some global object. Timer is a better option.