how long after brain death does cryonics become senseless?

[RibJig]

seeking opinions based on science as we now know it or as we now anticipate it in future;
my brief non-scientific search indicates a delay of 2 hours between death & cryonics is senseless ie brain is "annihilated"...?
even 1 hour delay is very very iffy...?
so if I want contingency in my alcor member cryonics contract to cancel service due to too great a delay, how much
of a delay should I specify? ($$ goes back to spouse or whomever)
as advanced as science may be in 2622 or 3122, a revived consciousness from a "spoiled" brain will never be possible?

[johnkclark]

The simple answer to your question is, nobody knows.

John K Clark