Some cells are still technically alive after 1 hour mark in the sense that there is no necrosis and cell membrane is still operating. This depends on cell type and nourishment - for example cells that have high amount of CoQ10 can live longer etc.
In any case, brain is definitely NOT 100% dead in a sense that ALL of its cells are necrotic which might explain why it is in a dream like state.
Also, I doubt 1 hour mark is regular thing in NDE.
Besides the clear possibility that the memory forms later, the brains of people who report NDEs have never stopped - there is no report of anyone ever recovering from brain death (as in, from a basically flat EEG).