this from a REMARKABLY (though unofficial) informed website dedicated to hypertime:
Here's what we know about the Crisis, step by step:
Before the Crisis, an infinite number of worlds existed in one "central" DCU timeline.
The Anti-Monitor sought to destroy this Multiverse with an anti-matter wave.
The universes within this Multiverse that were not destroyed outright were merged to become ONE SINGLE UNIVERSE again.
Shortly after the Crisis, DCU history was retroactively altered so that there was NEVER a Multiverse.
The last point seems to contradict what I said earlier about the Linear Men having record of the Crisis, but not really. It's similar to have a sentence written on a piece of paper, and taking a photograph of that piece of paper. If you erase the sentence, it's the same as it never having been there. But you still have the photograph, which contradicts the physical evidence of the blank page. The records at Vanishing Point (the HQ of the Linear Men) show a crisis in which 10 billion years of infinite histories were condensed into ONE history, but this contradicts 10 billion years of actual history that NEVER had a Multiverse. So, even though the Multiverse NEVER existed, it DID exist. If this seems paradoxical, don't worry, it's SUPPOSED to be. I don't believe the pre-Crisis Multiverse is *technically* reachable through Hypertime.
The Crisis DID effectively wipe out the Multiverse contained within the previous 50 years' worth of DC Comics stories. BUT, keeping in mind that there are an infinite number of timelines out there, there are undoubtedly Hypertimelines where the Crisis did not happen and the Multiverse (similar to the one we used to read about) lives on. And all of those pre-Crisis-type worlds ARE accessible to modern DCU characters.
hypertime>multiverse? who knows, but again, just because dc's cosmology is different from marvel's does not necessarily mean we can say marvel's cosmics are "greater". marvel seems to have an infinite amount of lakes, while dc has one infinitely large ocean with hypertime running like an infinite current through the middle of it.
darth was right -- the ONE universe DID get split into myriad planes, but even since then dcu cosmology has been altered.
dc is HARD to figure out . . .
🙁