For the record, you can do Triple Crown by yourself as well, I just got it. Did chambers 2-4, the latter two were cake and chamber 2 wasn't terribly difficult. I'm pretty sure the timer stops as soon as you solve the chamber, before you go through the door. Because I finished with chamber 4, and the achievement popped as soon as I dropped the safety cube in the hole.
"Man is only separated from Heaven by that which he will not ramp."