2-3 hours of writing, another 30-60 minutes of editing.
I always try to balance quantity and quality. My readers prefer 3 chapters to 1 chapter, which is marginally better than the others. At some point, you just need to release what you've got. Most readers care about the actual plot and not about technical writing abilities. Just make sure you are happy with the plot, there are no mistakes in your chapter, proofread it once, and then release the damn thing.
Of course, my opinion is only about webnovels and not classical writing....