I just spent an hour and 35 minutes working on a scene that just needed some attention.
If I'm focusing on my edited page count alone, I have reason to feel discouraged. However, it's a good edit, and the elements I added did three things. First, the character now acts instead of waiting for the danger to leave. Second, he doesn't get out of the conflict in the slick way I wrote into earlier drafts. Third, the threat in this scene now continues to plague him and influence his actions in later scenes. These are important changes. It's a good scene (in my opinion, of course).
So it doesn't matter.
Except to the part of me that is dying to get this draft done.
But anyway, editing is the time for spending 95 minutes on one scene.
What about when you're writing?
When you are crafting your first draft,your goal should be to write without letting the editor in your head take too much control. A quick write for something like NaNoWriMo is a good way to get past the paralyzing need to get it perfect and instead just get your story on paper.
For me, this can me I worry less about what author Louise Plummer calls "Precious" prose and more about the plot. It's a great exercise, and the story I'm working on now came out of a November NaNo.
Still, sometimes you just need to get a scene right. Maybe there's a picture in your head you need to capture now, or something your character needs to experience before the book can progress.
If this happens, savor what you write. Even if it's only a couple hundred words. Since NaNoWriMo lasts for a whole month, you'll have plenty of days to recapture your desired word count.