The first chapter is always the hardest.
To declare finished.
I'm plugging away at work on my sequel and today sat down for two hours to almost completely write chapter one. It was much needed and I think will work a good deal better... but I'll have to see if I still feel the same way in a month or so.
In a way I'm glad that I have a chance to get seriously started on my sequel before the first novel gets picked up by a publisher. As I work on the second book I'm finding several issues (most in relation to time travel mechanics) that need to be tweaked, changed or deleted completely in both books. So in the long run the entire series is going to work better because I've been able to venture further into the story before being forced to lock all of the time travel rules into place.
Seriously. Time Travel is fun, but you absolutely positively have to create solid rules that you understand and can explain coherently otherwise it completely falls apart as a concept. Timeline and the first 4 and a half seasons of LOST are good examples of well-written time travel. The last season and a half of LOST is how time travel absolutely positively should not be done. The Time Traveler's wife is a good story of a self-contained circle. Doctor Who is all over the place, with some episodes serving of examples of brilliance, and others as a glossed over mess.