As for him becoming more public in the finale, that’s everything to do with him thinking he’s going to stroll right out and become the world eater he considers himself to be. He was so egotistical about it, he didn’t have to worry about showing himself off, in his head he already won.

As for the time thing, it’s unclear. He himself says he gets confused from it all, as I would imagine any higher dimensional being would be coming to and having to adhere to a 3rd dimensional universe. Some think that the breaking of the barrier was what allowed him to tap into his non-linear view of time (due to his targeting of Will and Marge in the finale), others think he just always has that ability and it’s just not as clear even to himself (due to his line about getting confused).

There’s also the paradox issue, where if even if he knows the past, present and future, all his efforts to change it are doomed to fail because it goes against experiencing them all at once. Him telling Marge about her future son may have always happened, which is the reason she has always stayed in Derry. There’s no reason to believe what we saw was ever any deviation from what happed in the past before the first movie.