For hard boiled eggs, bring to boil, time for 12 min (I do not like mine wet at all in the center) but DH loves his 2 min egg mashed over toast.
If it was for Canary baby food then they were cooked 20 min to ensure sterilization. I do not think there is an exact science to the process, trial and error to what suits your taste.
If you have our type eggs, less then week old (gulp and gag) you can use them raw, eggnog etc. YUCK....
Thanks for posting this one.. my mom has always laughed becasue for some reason, my mind refuses to store egg-boiling information!! I have had to call her EVERYTIME I boil eggs to ask how long, ect... Now, I just look it up on Google!