My recommended one-shot length depends on how long the work is.
1K - 5K
I would say that this should be about one to two paragraphs long with around five sentences in each paragraph. 3 if you're a chronic run-on sentence writer (guilty)
6K - 10K
3 paragraphs to an entire page in Google Docs (my form of reference lol)
11K - 20K
We are in two pages of introduction territory, at this point, you already know this is a monster, that's like a whole 2K words of introduction right there
21K +
First of all: you are deranged (just like me) second of all: three pages and up