Doctor Manhattan

In Before Watchmen: Doctor Manhattan, Jon attempts to look back before his conception as Manhattan and creates an alternate timeline where he never becomes Doctor Manhattan and the world ends. The end of the comic sees Jon in a new timeline, the DC timeline, as I like to call it, the world of Before Watchmen, the original Watchmen, and Doomsday Clock. In this case, shouldn't we have pages for both the original Watchmen timeline before Jon looked back, and the alternate timeline he created by accident? I think yes. As for names, "Watchmen: Manhattan Timeline" for the accidental alternate timeline, and "Watchmen: Original Timeline" for the original timeline.

I'm really interested in Doctor Manhattan, but besides Watchmen I don't know what to read.

I saw HBO's Watchmen recently, having no clue about any of its story and not read the graphic novel or watching the movie before watching, and now I'm confused.

Dr. Manhattan experiences time all at once and he can see the events of the past and future and he knows what's going to happen but he can't change it? E.g. He and his wife know they're going to have an argument and they try to just stop talking but it happens anyway? So it means that in Watchmen universe events of the timeline are rigid? How can this concept of time exist in the DC Multiverse where alternate timelines also exist and people with the knowledge of the future or past change the timeline like all the time?