Wyverns lose 1 good point per 10 seconds, and 360 points per hour. So 1 wyvern milk will sustain a wyvern for 3.33 hours due to it's 1200 food points. If it's a low level, it might not have 1200 points and have to be force fed milk to avoid starvation. But once you feed it milk and it goes up 1200, you can safely walk away for 3.33 hours and return back to knock out a wyvern and feed it after. If you want to imprint, that's a different story. (The same wyvern can be knocked out for 5 milk every 1 hour). Preserving bin + preserving salts for milk = little over 2 hour spoil time. Good luck getting a wyvern! P.S. make a wyvern trap. It's the best method for getting milk. :)
I got a level 150 lightning egg and I was so excited to hatch the egg...that when I went to put the egg down I accidentally ate it instead. :( ps4 users: R2 ISN'T GONNA DROP THE EGG YOU'RE GONNA EAT IT LIKE ANY OTHER EGG. REMEMBER THIS. LOGIC BEFORE EXCITMENT.
Good way I've found to get wyvern milk is lure a female wyvern out into the dunes on scorched earth with your own wyvern and shoot the wild one to knock out as it attacks yours(by the way it is quite risky and when I did it my lightning wyvern died and I was so angry with the poison wyvern that did it I forcetamed her and found out she was much better than my last so worth it in that way too👿)