That makes no sense. Refrigerant has oil in it, it doesnt dry out seals, and how does the a/c off 30s early to "drain" any different than shutting the engine off.On an A/C note, if you never want to have to service the AC unit in a vehicle, turn off the AC control 30 seconds prior to shutting down the engine. It allows the refrigerant to drain back and not remain in the lines, drying out the seals.
It works - we've done this with a '92 Blazer (had 8 years), 97 Contour (had 7 years), 2000 XJ Cherokee (had 15 years), 2007 Saturn Ion (had 13 years), 2015 KL Cherokee (have now for 5 years) and not one was ever serviced once. Coincidence is unlikely.
however, it will help with mold growth in vents if you shut the A/C off and leave the blower on. a few mins before parking.