It is gathered by collecting it from the inventory of wild unconscious female Wyvern or dead Alpha Fire Wyvern of either sex.

Get like 8 of this stuff and you should be good for one baby wyvern

Lasts 9 hours on scorched earth in a preserving bin with the addition of preserving salt.

In ragnorak milk lasts 1 hour 49 min in dino inventory

This can be stored in a tek trough to extend the timer to 2 days by putting the milk on a storage box on a platform cart

If you knock down a female wyvern a second time, it wont give have the milk in the inventory even if you did not get it the first time.

Mil lasts around 26 minutes in the inventory. Or about 1hour and 45 minutes in a dino's inventory.

It can only be tamed from knocking out a female wyvern at least that’s what I heard

Apparently alpha wyverns give a lot of this