When time ends, a new universe is formed. A multiverse is not certain. Paradoxical events, like the Sundering, are necessary to create a multiverse. The dimension at the centre of the multiverse is FirstWorld, the original universe. It is not known whether the multiverse is infinite and this is a major bone of contention between scholars. There is an argument that an infinite universe could never tip fully to Law or Chaos and so in an infinite multiverse time could never end.
This multiverse is relatively young (the Sundering occurred in Year of Creation 19231 which is around 207,000 years ago in this dimension). However the universe it came from is very old.