So at one time there were a few people not many though at least I don’t think saying that there might be some time travel in Halo Infinite I don’t think there will it would not fit well in to Halo Infinite but if there is there is still a way to save Cortana
People speculated about time travel years before anything solid was shown for infinite. It was one of those rumors that got thrown around a lot. Much like how Halo 6 is going to have space travel to other worlds just like destiny and your supposed to be able to do them in any order you want. 
From the direction of how things ended I don’t think they’ll be doing time travel. The very end did have Chief and Weapon show up somewhere on the ring days later after defeating the Harbinger. Kinda time travel, but only in the since that time passed for everyone else, but it didn’t for them. Which is a theory for how time would pass for those moving near or possibly beyond the speed of light through normal ways of propulsion. Anyway, it seems like they’re just going to move forward from here with Weapon or whatever her name will be once the first campaign dlc happens.
Hate to break it to you, but watch the legendary ending cutscene.
Um you mean us seeing atriox releasing the endless as an exert from a book was read out? That ending? Talking about Offensive Bias being deployed? That ending that I clearly understood all the information of? That legendary ending? Which had nothing to do with time travel or anything like it? That ending?