It's a bit more than a hentai doujin and certainly mone than a few paragraphs.
For instance, some numbers I recall off the top of my head, Noire, the sheepgirl from the baths, was 200 pages. Tatsuya, the male Kiyoko type character Jstar was working on, was commissioned at 20k words ( but is quite a bit longer, apparently).
We had this discussion a month ago, and I found a website that had a bunch of both professional and semi-professional authors on it, and most of them recommend doing around 1000 words per day.
So a month to write a very basic character with few to no variables, a month for review and editing, and another month to make it through the coding queue - three months from farm to table?
Note: I'm 100% guessing, I have no expertise, just what I've observed from being around these games for awhile.
From what Ive read, part of the issue is with visibility of the content. A character that accounts for a bunch of variables and differences might have a scene that's 200 words but took 300-400 to type because of the parsers they work with. So often it can look like there's less there than there is.