Normal flight below 370, no. I don't wear it. Above 370 it is out of the carrier. I don't believe any contortionist can reach a mask in 5 seconds, time your self in the plane at cruise. Out of the blue scream at your copilot " get your mask NOW!" (Don't forget to video it so we can all laugh later)
Installed (certified part 25 plane) bottle is only big enough for emergency descent/smoke. No using it for a 3 hour flight above 350.
In Normal mode the mask will still use O2.
Been to 510. Masks on. 100% pressure breathing. Had an empty plane. Empty, cold, and out of gas is the only way it will get there. Not really practical. The overspeed/stall tapes were close. Got a picture somewhere...
470-490 was not uncommon, but the boss did NOT like being up there. He read enough to realize how inhospitable that environment is.
Mask switched to normal won't help you up there. Yes the mask is supposed to automatically switch, but if you are going to have a bad day, it will probably fail to.
Above 410 one mask was out and ready. Above 450 one mask (Eros) was around the neck. The SMALL bottle the manufacturer installed to meet the certification/survival requirement does not have enough air to cruise with mask delivering for the duration above 410, let alone 350. You have to have the minimum for smoke/fire to get the plane on the ground.
A better question is " in the sim, when you do rapid decompression/emergency decent, when do you take off the mask." The correct answer is "when the aircraft is stopped on the runway so I can get out." But no one does that in training, so we will fly like we train.
Explosive decompression isn't the issue. A gradual increase of cabin altitude leads to the euphoric hypoxia that prevents the ability to place the mask on and use it. A Lear 31with the bleeds off will make it to 230 before the cabin warning goes off. (Or so a bird told me). Mask goes on pretty fast. But The cabin was at 15500 before we got a horn. Not really where it was supposed to go off.
Remember these rules were made a LONG time ago. Believe it or not, airplanes were flying a while before anyone decided to stick a computer inside to make a pilots life easier.
At 470-510 an explosive decompression is going to freeze your eyeballs and another point to consider is that lovely mask you are counting on is probably only certified for use below 410 (the newer ones are 450). The reason themanufacturer gets away with that slight of hand is showing that the aircraft can get below 410 BEFORE the cabin gets to 410.
Put the mask on in flight, do it enough to realize that glasses are in the way, the headset really slows down getting it on. Breathe with it. Do dearth Vader. Figure out how to get the mask held to your face and drag the straps over your head. Then hope you never need that knowledge, kinda like V1 cuts...