B738 flight crew oxygen requirements

[carnival30]

Hello
I know this has been discussed earlier but the right answer still not found. I have seen people saying refer to MEL/FPPM but I could not find any there except minimum dispatch pressure which can be checked against bottle temperature for the day. My questions:

1) Pax get 12 mins generally (or 22mins). What about flight crew at 100% selection? QRH says set the regulators to 100% O2. So from the moment of donning/wearing how much time we are left with the flow of O2 (76 cubic feet cylinders)?

2) Is there a regulation that by how much time we have to come down to 14,000 or 10000 ft? If we cant descend to 10000 ft due terrain then how long can we stay up to 14,000?

[autoflight]

Whatever your regulations, be sure to not run out of fuel (due lower altitude) or hit a mountain (due fixed idea that 10,000 or 14,000 ft are safe). Unless there is smoke or fumes, when your emergency descent due to pressurisation failure is completed, O2 is no longer required at 10,000 ft and would normally be turned off. Your emergency descent may be substantially complete but needing to remain clear of very high terrain. At some time during extended flight above 10000 ft it would be prudent to select normal flow to conserve crew O2. QRH is "quick" and your operating and training manuals may give further guidance. If your airline regularly operates over very high terrain there may be a detailed company procedure to cover this case.
If guidance is lacking, you should study what you would do with an open mind about the possibility of a flight at night or IMC or the chance of VMC day where you may be able to safely descend visually to 14,000 or even 10,000 even when the flight plan min safe altitude or grid MORA is very high.

[FlightDetent]

Common rules (not sure about yours in particular) is for a 737 size A/C, there's 30 minutes time from 14000 to 10000.

Crew supply would not last the prescribed 120 minutes on 100% (which is the default for the smoke/fumes case). Somewhere deep in the manuals, it should say to switch to NORM eventually.