Bonsoir Zearos
As previously said, you can evolve them after every lvl up you make.
I want to add, that you can't evolve Pokemon, which require a lvl up to evolve, if they are lvl 100 (There is no way, even staff won't help you).
It's better if you evolve them early (lvl 95-98 , when you will use Rare Candies). It's really annoying to have lvl 100 Pokes which are not fully evolved. :Cry: