This question apparently doesn't have a single correct answer: What are some monsters that could trap NPCs for a long time without killing them?
On the other hand, it is pretty narrow for being "idea generation". Is this question on-topic?
Related: How can we distinguish "idea generation" questions from "asking for a solution" ones?
Very borderline but possibly salvageable, IMO.
I think the current phrasing of things, especially the title, does veer too close to idea generation. "What are some" is a yellow-flag of a phrase, but not always unrecoverable.
If the core question is, "Due to a time dilation effect, I need ways to hold human captives for excessive amounts of time without aging and dying", as I read it, that can be made stackable by limiting to published sources and doing a phrasing tidy-up.
