Not sure what you mean by that. It's a chemical generator, not dependent on pressure altitude as far as I know. When the chemical reaction is over, no more oxygen.
If it were liquid oxygen supplying the masks (an option on the 777, but I don't think MH had this) then the oxygen for the passengers lasts longer with higher altitude (assuming they can stay alive with the lower partial pressures).
I don't think the pax lasted more than 30 minutes. The flight attendants probably a lot longer on the walkaround bottle -- but not for 7 or 8 hours!
Like you i have no idea what one has to do with the other and its the first I had heard or read that. Am sure it was talked about in class at some point, but again the brain does not think in those terms. I am going to be getting the hell down.
You mention no flight attendant could last 7 or 8 hours. Which now i am giving more thought. Actually yes it could happen. Let me try and explain. In the best case scenario, as you say no passengers lasts for more than 30 minutes. One, possibly two cabin crewmembers get on an portable oxygen bottle (as in the Helios 522 accident) which dependent upon flow lasts from 30 minutes to 1 hour.
Here is the kicker . . . The oxgen bottle in the cockpit only lasts 30 minutes. Or thats what we plan on. Of course many factors determine the exact amount. Probably longer. But by regulations at least 30 minutes.
Of course, if one really wants to play the game, one could say the pilot himself could have gained access to a portable oxygen bottle and last longer.
So since we are playing the theory game, it is conceivable a cabin crew member on a portable oxygen bottle can last as long if not longer than the cockpit crew. IF the pilot removed oxygen from the plane to kill the passengers, he himself only has 30 minutes of oxygen. So at some point if he wanted to remain alive, he would have to re introduce oxygen back into the plane.
IF he re introduces oxygen back into the system, any surviving crewmembers on the portable oxygen bottle could survive for the duration of the flight.
If he chose to kill himself also by not re introducing the oxygen and just let the plane fly forward, a surviving cabin crewmember could have gained access to the cockpit as the young man did in the Helios 522 crash, but not know what to do. And you are correct, run out of oxygen at some point.
In the Helios crash, they found all the portable oxygen bottles had been emptied. So at least more than one cabin crewmember got to them. I figured the surviving cabib crewmember used two bottles for himself to last as long as he did.