Sorry to drop in here, but I had a question that's been on my mind lately and I wasn't sure where to ask it? It's not super serious.
In Star Trek: Generations, Picard is taken up into the Nexus and asks to be taken back to stop Malcolm McDowell on the planet and that's what happens, but as far as I understand, the Nexus doesn't give someone the power to travel in time. I know it was used that way in the movie so that we could see the consequence of McDowell's plan and then Picard can go back and stop it from happening, but nothing else in the movie suggests that it is possible to use it that way (at least no one else did). I know that all of this happens because Generations is a bad movie, but since that movie is technically "canon," is it possible that everything that happens after Picard talks to Guinan in the Nexus (mainly the events of the other TNG movies) is a hallucination of Picard within the Nexus? Is he still trapped there?
I think the idea is that time has no meaning inside the Nexus, therefore anyone who enters the Nexus (at any point in time/space where it exists) can exit the Nexus at any point in time/space where the Nexus exists. There are very few examples because very few people have gotten in there.
Guinan and Malcolm McDowell successfully entered the Nexus, but then they were pulled back out. = No time travel.
Captain Kirk successfully entered the Nexus, so (with Picard's encouragement) he exited the Nexus in the 24th century. = He time traveled forward.
Picard successfully entered the Nexus because he was next to Malcolm McDowell when McDowell worked his plan to re-enter the Nexus. On the advice of Guinan, Picard exited the Nexus (with Captain Kirk) five minutes in the past, because Guinan told Picard that time travel should be easy for anyone who willingly leaves the Nexus. = Picard did just a little bit of time travel backward.
The Guinan that Picard talked to in the Nexus was the Guinan who was inside there for a few moments. She couldn't exit the Nexus because she already did exit/was going to exit. But time is meaningless inside the Nexus, so Guinan's presence inside the Nexus is infinite. As is Kirk's, and Picard's, and Malcolm McDowell's. Malcolm McDowell will always be inside the Nexus, but he can't stand life outside of it, so going back in, or dying, whatever, it's all the same for him. His outside life must end, and his inside life was always infinite and never in question. His plan was pointless, and he should've just killed himself.
Picard exiting the Nexus in the past seems to have pulled Malcolm McDowell's body back out of the Nexus, unless it changed time and prevented him from getting in the second time. But that seems like an irrelevant detail because it doesn't change anything about Malcolm McDowell, except to suggest that maybe he has a second real body loaded into the Nexus, capable of exiting, but Malcolm McDowell would never use it as the Nexus is paradise and he doesn't want to ever leave the Nexus.
But Picard exiting the Nexus in the past seems to have overwritten the past Picard, otherwise there would be two Picards.
And yes, it is possible that the ending of Generations and everything after that movie was all a dream, because Nexus-Picard dreams of starring in bad action movies and "old Picard" TV shows produced by Alex Kurtzman, but nobody likes those "it was all a dream" fan theories.
I always thought it totally allowed travel in time. I took Whoopi literally when she said "time has no meaning here" and that's why from their perspectives Kirk and Picard arrived in the Nexus at the same time.
The Kirk and Picard who left the Nexus are the Kirk and Picard who didn't spend much time in the Nexus, that way they didn't have much of a chance to get addicted to the Nexus and were able to survive on the outside and didn't go all Malcolm McDowell.
But since time is meaningless inside the Nexus, Kirk and Picard are essentially still in there. As is Guinan. As is the cool Malcolm McDowell who first got in there, before he got pulled out and went into crazy withdrawal. And maybe the crazy one too, since he did or didn't get in there a second time. They're all hanging out and partying until infinity.