Anyway, the key to how Bill and Ted treated this comes both with the stuff with Ted's father's keys and the stuff at the Circle-K. There's a minor plot thread in the beginning of the movie with Ted's father looking for his keys, we later discovered that Ted stole them by going into the past at some point in the future, stealing them, and hiding them for him and Bill to use to save the historical figures. Then, of course, we see Bill and Ted arrive at the Circle-K and the interaction there before Bill and Ted have left, or even realize what is going on.
Good stuff here. I followed you perfectly through all of this, and was thinking about the keys when I wrote about the "Bill and Ted theory of Time Travel"
(which was also used in the sequel, and I agree that Bill and Ted is only time travel story I can think of that used this "single timeline" idea. I also agree that, for some reason I can't describe, it seems the most sensible "logic" to me.
My question is: can you add more context to it's use at the Circle- K? I don't quite remember how this logic is sued there. I haven't seen the film in a while.