I have a general idea of what's going to happen in the story and some of it is scripted, while some still need to be. I thumbnail about 10 or so pages in advance then draw them from there. Rinse and repeat. Thumbnailing doesn't take too long. Probably an hour or two, depending on how many I'm doing.
The actual time it takes to work on a page is about 6-10 hours, give or take. For me, lineart takes FOREVER to do (like, 60% of the time I'm doing lineart....). This is why I don't even bother cleaning the lineart. In my comic, everything looks sorta sketchy, but I like it that way. haha. Coloring also takes time. I'm not very good at it. ^^;