They don't...at least not at the schools I have been to there including two M-schools. In the show they used a timer to accurately time everything while at the schools they use a stopwatch, so accuracy is not so great. The only thing I've ever seen timed there were autocrosses, and they also used a stop box in each of those as opposed to a flying finish like in this show (and like all "normal" autocrosses).Without spoiling the winners, and presuming Spartanburg standardizes some of these competitions:
Slalom in 8.26s, was a record.
Autocross in 39.49s.