Roger, according to Wikipedia, time of useful consciousness (TUC) at 22,000’ could be as much as 10 minutes (normal ascent) or as short as 5 minutes (rapid decompression). At 35,000’, those numbers are 30-60 seconds and 15-30 seconds, respectively. And at 40,000’ the numbers are 15-20 seconds and 7-10 seconds, respectively. While unconsciousness certainly occurs quickly at the higher altitudes, many stowaways have survived several-hour flights in the mid-30s. I imagine the outcome isn’t as good after a couple of hours in the upper 30s to low 40s.