So after some testing and calculations, I think I figured out the food depletion times.

At the 'baby' stage(0%-9.9% maturity), the food goes down one point every ≈ 11.5secs ±0.1secs. So for example, 2000food × 11.5secs = 23,000secs ÷ 60 = 383.33mins ÷ 60 ≈ 6.38hrs.

At the 'juvenile' stage(10%-49.9% maturity), the food goes down one point every ≈ 23secs ±0.1secs. So 2000food ≈ 12.7hrs.

At the 'adolescent' stage(50%-100% maturity), the food goes down one point every ≈ 32secs ±0.1secs. So 2000food ≈ 17.7hrs. This is until fully mature.

(I did not check if the depletion time is different during 50%-75% maturity vs. 75%-100% maturity. I'll update this if there is a difference)

So with this you can figure out how long you can leave the rock drakes for and if you pair this with the maturity calculator, you can figure out how much food you need till full maturity.

Disclaimer: I ran a couple few several multiple tests to the best of my abilities and i thought I'd share it since I'm raising 29 rock drakes at different stages at the same time. However, a 0.1sec discrepancy can make a difference.

So when calculating and setting your timer, give yourself 1-2hrs of time before the food runs out so you can acquire nameless venom, maybe 3-4hrs if you're raising 29 rock drakes at the same time >.<