Time of useful consciousness at 35,000ft is not in seconds. For a start you have a lung full of air,
A lung full of very thin air - after you've forcibly exhaled most of what was in there during depressurisation - leaving you with oxygen rich blood (relative to what is now in your lungs). O2 will start to flow the wrong way out of your blood stream. Every breath you take will blow more O2 out of your body until you lose consciousness.
Its not like holding your breath under water.
That said - you will still get more than just a couple of seconds @35K, 30 secs, 45??