To continue from my previous formula of food x 10 or 45 ÷ 60 ÷ 60 one venom replenishes 400 food. At ~18% OF TOTAL FOOD is when my rock drake ate, for me this was 846/4800 but i read it would eat at 10%. Here's a simple formula to find when yours will eat based on 18% : (max food) x 0.18 = eat.
They lose 1 point of food every 15 seconds, so to time how long until they start starving, multiply their current amount of food by 15 and then divide by 60 twice. This will give you the number of hours left untill the food stat reaches 0.
((15 x food)÷60)÷60
Obtaining this creature will require you to enter the tek trench where puprle liquid and the nests of these creatures lay past the bioluminescent chamber, there you must steal an egg and raise in a cold environment feeding it nameless venom you can get by killing nameless