That level uses a timer exploit, as does a few other challenges. Basically, as I recall on the top route somewhere there's a yellow timer, and a bit after that a checkpoint. The exploit is to activate the checkpoint, then backtrack, pick up the yellow timer, and kill yourself. The trick is that dying respawns the timer; the timer takes 10 seconds off the clock, while the loop from repawning, grabbing the timer, and dying can be done in under 10 seconds. So basically you have to pick up the same timer over and over until your time gets to 0:00.00, then continue doing it until you feel comfortable that you have enough time to finish the challenge before the clock starts ticking again.
I remember that one in particular being very not fun, but eh.
