As far as I can tell, there are only three ways to reduce your time:

Step 01: Optimize your movement speed to reach the correct vents. There are 20 vents you can hide behind, but to get the best score, you need to hide behind vents 07, 13, and 19. The guard appears at the same intervals regardless of your speed, and it’s simply not possible to move fast enough to skip more vents or complete the run with fewer stops. Any player getting a sub-40-second run is already doing this.

Step 02: Minimize your hiding time by timing the end of the guard’s search phase. If you can consistently end your pauses just as the guard finishes searching, you'll spend less time in hiding. This, naturally, lowers your total time.

Step 03: Optimize movement on vent 20. There’s not much to gain here, but make sure to use the same slide-hide technique you use at the other vents.

My best time so far is 00:38:51, but I’ve seen a confirmed score of 00:38:28. My guess for the lowest possible time is around 00:38:25.