How to?: ERZ3's Space Countdown Timer

ERZ3 has a space countdown timer that activates after a certain amount of time in single player and co-op. I've skimmed through the level trying to find the timer... except I don't know if there is a timer. or anything that acts like a timer in ERZ3 altogether. How does it work?

The control sectors responsible for this are right next to the starting area. There's an intangible, invisible FOF with the space countdown effect and tag 65535 (so it's laid over every sector in the map). When the level starts, the FOF has a floor and ceiling height of 2112, which is higher than every ceiling in the map. Then there's a delayed linedef executor that's triggered once the player enters the sector with the spawn point (so basically at the start of the map). After 2905 tics (83 seconds), it lowers the floor height of the space countdown FOF so that the entire level is covered in it. This wiki article tells you how to set up delayed linedef executors.