For example, in Those that disobeyed were frozen in place for all of eternity. how should I translate eternity? Specifically, how do I translate it in the context of a small eternity?
That's just eterno.
Tiuj, kiuj malobeis, estis fiksitaj surloke por ĉiam. / por tuta eterno.
"In place" is surloke or enloke. If "frozen" is literal, then use frostigitaj.
I suppose "a small eternity" would be an eterneto, but that sounds a little too much like Eterreto ("Ethernet"). Maybe an eta eterno?
I would say "eterneco" - "eterna" (eternal) + "-eco" (state, quality).
I'm not sure what "a small eternity" is even in English, so I'm not sure how to translate that one.