You will pass out in 15 seconds no matter how calm you are. Then, after 4 minutes without oxygen you will begin to suffer brain damage. The oxygen generator the mask is connected to generally supplies about 15-20m of oxygen which is more than enough as it typically only takes 2-4 minutes for the emergency descent the pilot will do after loss of cabin pressure, this is of course, assuming the pilot is still conscious himself. There are numerous accidents where the pilots themselves delay putting on their oxygen masks with disastrous consequences, because your critical thinking and reasoning skills hit the floor within seconds.

The main point of the oxygen masks though is primarily to keep all passengers alert and ready as it is essential that at all times an evacuation can be performed in under 90 seconds. When the passengers are not able to reason correctly due to hypoxia, that's effectively impossible. This is what could kill you and your fellow passengers if you fail to put on your oxygen mask in a pressurization failure incident.

Which incident are you referring to with the oxygen generators igniting? Not this one I hope?

https://en.m.wikipedia.org/wiki/ValuJet_Airlines_Flight_592

> However, the NTSB quickly determined that just before takeoff, 144[15] expired chemical oxygen generators, each slightly larger than the size of a tennis ball can, had been placed in the cargo compartment in five boxes marked COMAT (company material) by ValuJet's maintenance contractor, SabreTech, in violation of Federal Aviation Administration (FAA) regulations forbidding the transport of hazardous materials in passenger aircraft cargo holds.

Because that's not exactly the fault of the ones that were installed on the plane itself.