Getting out a new chapter, I'm so darned slow. I tend to write 1000-2000 words a day, which takes anywhere from 20 minutes to an hour. But I have a long editing process. I'd say, hmmm...maybe 8-16 hours of editing for a chapter, depending on how much I need to change, rewrite, cut and rewrite, etc... So, say, average of 13 hours to finish one chapter? That'd be my guess. Every once in a while I get lucky and it just comes out perfectly, but that's rare for me.
As for finishing a story that's gotten boring? Oh, hard one! I do tend to have other ideas pop up, a lot. And at first, I started writing a few of them. But now, I just record the idea and sit my butt down and finish the one I should be working on.
If I am REALLY not feeling like finishing, I'll set myself very short term goals. Like, set a timer for 10 minutes and then write as many words as I can on the unfinished story in that time period. Then do it again. And again. Maybe reward myself with something afterward, if needed. That's what gets me through, typically.
Usually, the writing is utter crap, I'll be honest. But at the same time, as I've heard said, I can edit crap. I can't edit a blank page, ya know? It takes me longer with the edits, but it gets done. :-)