If u have offline protection simply put 5 or more milk in its inventory make sure it has at least fifteen minutes on its spoil timer( easy with pres salt) then log out for 49hrs then when u log back in it will be fully grown and u can just use it to get a better one. Or if not make sure to make a pen/nest(sounds cooler) in a very unlikely place for a player to be (top of mountains) and hatch it there. If no players are around it it eats 10% of the normal rate of food allowing feeding roughly once every 7-9 hrs
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.