Sara, I agree that Henry couldn't control his time travel. I guess I meant that it seemed like maybe sub-consciously he made it happen, or by really wanting it to happen. It isn't essential to the story, though. I just like the idea that maybe for really important things he could influence it a little bit.
The list of dates is actually the classic example of a time travel paradox, and the author wisely avoids discussing it, other than Clare saying "it seems like a Mobius strip." In chronological time, she writes down the dates in a book at the age of six as Henry recites them, meets Henry on all those occasions, then hands the list to Henry when she meets him in real time. He memorizes it, and later travels back in time and tells them to Clare at the age of six. Once it is in place, it works, but there is no good way to get that circle started.
I think he felt he needed to tell Clare about getting married one day, since he was going to be visiting her a lot between the ages of six and eighteen. She needed to know what was going on.
Steve