Hello, I always find it easier if I break a project down into manageable chunks with specific timescales - the daft things I used to do included having to get to a page divisible by 40 on the last day of each month (ok so bordering on OCD, but it did seem to make the task fly by). You may also be thinking that the second book will be a longer slog than the first, but you may just find that you slip into your own style of writing and become engrossed in writing so much that it doesn't seem as much of a chore.
Don't forget if you're worried about the direction your new book is going in, whilst its so exciting and fresh in your mind, there are plenty of people on here who can offer hints and tips (crikey don't ask me, I've just finished a cookery book, it was easier to get motivated with each recipe, as I was usually hungry and desperate to eat it).
I don't know if you've managed to suss out your working pattern. When I was studying, I'd take time off work to complete assignments, and watch daytime telly and clean the house until about 8pm when all hell broke loose and I'd write until midnight - after a while I just accepted that no matter how hard I tried, I'd never be the sort of person who could write during the day, always a night bird. Mayve try to write at a different time, get comfy.
Hope it helps - Cath