Time CONCEPTS, not vocabulary to the Na'vi

[Niri Te]

Oeya yawnete, ateyo te Syaksyuk and I are writing a pretty good fan fiction that takes place eight years after the RDA Vrrtep are thrown off Pandora, that she is posting on LearnNavi.
We are at a place where the concept a long time span is going to have to be explained to the ayeyktan of the different clans. We know that the word zisit
(year) exists, but do the Navi have a "feel" for that? We will be talking to them about the 250 to 300 years that it is going to take the Earth to turn it's almost runaway greenhouse atmosphere around, and need to know the orbital period of Pandora's Planet around the star, can they conceive of an Earth year, or should we measure long time spans for them in either Generations, (is there a word for that?), or lifetimes?
Thanks for your help folks.
Niri Te