The Talmud Bavli, Suka 46 amud 2, cites a difference of opinion as to how long an esrog and a suka are muktzim l'mitzvosehem, set aside for their respective mitzvos and forbidden for use for other purposes:
R. Yochanan said: An esrog is forbidden for personal benefit on the seventh day [of Sukos–Sh'mini Atzeres] but permitted on the eighth; a suka is forbidden even on the eighth. Resh Lakish said: An esrog is permitted even on the seventh.
Rashi explains that Resh Lakish holds the esrog is permitted for benefit straight after it's been used for its Mitzva.
It's not clear (to me) from the Talmud and Rashi what Resh Lakish holds about suka. However, from the wording quoted above it seems to me that he agrees with R. Yochanan. Moreover, my kid assumed (or learned?) that that's what Resh Lakish holds.
The Talmud continues:
R. Papa said to Abaye: According to R. Yochanan, what's the difference between esrog and suka [that the latter is permitted on the eighth day and the former is not]? He told him: A suka, which is fit for twilight (if he happens to have a meal [then], he must sit in it and eat in it), is muktza for twilight, and because it's muktza for twilight it's muktza for the whole eighth day. An esrog, which is not fit for twilight, is not muktze for twilight, so is not muktze for the whole eighth day.
My kid asked:
According to Resh Lakish, an esrog is forbidden during twilight at the start of the seventh day, yet becomes permitted during the seventh day. Yet a suka is forbidden for use all of the eighth day because it's forbidden during twilight of the eighth day. What's the difference? Why isn't a suka permitted for use after its usage time is done, i.e. after twilight, just as an esrog is permitted for use after its usage time is done?
I will be glad to learn that Resh Lakish in fact does not agree with R. Yochanan about suka and holds that it become permitted for use after twilight, assuming that someone finds better evidence for such a claim than the wording of the Talmud quoted above or the existence of this question (or ones like it).