If using the incubator for Griffin eggs i found the right temperature is 17.0

Ragnarok on ascended you can breed griffins now. Egg counts as a superior egg for kibble

The griffin egg can be used to make griffin kibble to tame a UNICORN! A very rare creature and only spawns once on the map and is hard to find, but wild griffins do not lay eggs only if you tame one or breed one.