Answers to your questions, if you want them. You can decide when/if you read them:
massive spoiler blocks incoming two posts even
Why they don't time travel (I... don't think they touch on this directly really but you can definitely reason it from the existing technobabble): The energy cost to do such a thing is extremely high. They managed it in Chapter 8 because Zill had brainwashed the entire population with Sharl which unified their feelings and hijacked her song using that. Without that, it's highly unlikely you could get the entire world's population to truly and sincerely wish for time travel back. Plus, in Chapter 8 Clacket outright states that it's cool if they sacrifice Ra Ciela as fuel for the time travel on top of that. If it goes wrong you probably end up destroying the planet and/or killing the singer with no results. Keep in mind Revelt just wanted a third dimension shift (physical teleportation) for a few hundred people and was basically going to destroy Ra Ciela for that. Time travel is 4th dimension so the cost goes up. They just don't feasibly have the power to do this unless they want to gamble with the lives of everyone on Ra Ciela and Ra Ciela itself. And without the "well Nero broke reality, let's go for it/Oh Nero broke things, let's fix them" rationalization. On top of all that, as Nero showed, messing around with axis shifts is just inherently risky anyway and the higher up you go the worse it gets. Ion was simply correcting Nero's error before. A hypothetical shift now would once again risk breaking reality even if perhaps not as catastrophically as Nero did (or maybe worse! You won't know until you try!) ---
xp1337: Don't you wish there was a spell-checker that told you when you a word out?