Timers are similar to counters, except they are the opposite (they count down instead of up). They also can be displayed on the screen.
First set the timer for a certain number of seconds by the B7 command. Then start and show the timer by the B9 and B5 commands. You *can* start the timer but not display it on the screen, for a silent countdown, using the B6 Hide Timer command.
Now loop and detect if the timer is below a certain point. To detect if it reached 0, detect if it’s less than 0001 using the BB command. Finally, when it return value loops successfully, which means the timer is where you want, you hide the timer using B6, Stop the timer using B8, and then do whatever you want.
In this case, we choose to fail the objectives by doing command F9, then exit the level using command D2. And to be safe, we do 05FD0001, although it’s probably unnecessary.