By 'some time' I mean on the order of a few hours. This is drawn from a few things, notably people who have recovered from medical death under cold conditions after multiple hours, and the relatively recent discovery that most of the numbers originally thrown around for irreversible brain damage (three to five minutes) are actually due to cell suicide when the patient is too rapidly reoxygenated, and many brain cells may remain viable for several hours. Additionally, the synapses, which are our primary point of concern in cryonics, are less volatile than the oxygen metabolism of the cell proper, which are likely to be the first thing to go.

On the other note, a synthetic oxygen carrier / oxygen-doped particles would certainly be an improvement, if it's that effective. I wonder if it would be practical to keep a syringe on my person at all time, and wear a bracelet giving instructions for administration.