I’m no expert but used O2 for years in my Mooney.  In the Air Force chamber, we  blew from 18k to 29k instantly.  Most had about one minute of consciousness, some had much more—plenty of time to turn on a tank and put on a mask.  If no O2 one can dive 10k feet in a minute.  25k is nothing like 44k where the Payne Stewart Lear depressurized.  Those pilots didn’t dive, but fiddled with an empty O2 tank