I did the same thing but we used milk. It was not very fun, there were 7 of us and i came in 2nd. This was 7 years ago so i dont remember the exact time but it was under 20 mins.
If you plan on finishing the whole thing have a large trash barrel in front of you that you plan on getting rid of. It will smell of sour milk forever. You will throw up, a lot, fire hose style. You get really cold afterwards, i dunno if its because the milk is cold or if it is because you throw up everything that was inside you.
Good luck!
Disclaimer: I am not a doctor nor do i condone your actions