Is it possible for other worlds to exist after the Hour is established and entry into Paradise and Hell has occurred, and is it possible for other worlds to exist at this time?

There is nothing that definitively proves the existence of other worlds. However, some contemporary scholars see this as based on verses such as: "And He creates what you do not know" (16:8), and "And among His signs is the creation of the heavens and the earth and what He has dispersed therein of creatures" (42:29). As for after the Hour is established, there is no sacred text that clarifies this matter; it is among the unseen which none knows but Allah, and Allah is capable of all things.