I have Tricare also.
I am 5'1" - 220 lbs, with type II diabetes, I got my referal from my PCM on 04/15/2009. Saw the surgeon on 04/24/09. Got the medically necessary letter from the PCM to the surgeon on 04/29/09. Got my approval on 04/30/09 and was banded on 05/12/09.
Tricare is very quick if the letter say's the right things. They will also call you as soon as the approval occurs. You will know before the surgeon.
Tricare has two rules, either you are 100 lbs over weight or you have a morbidity factor and fall into the obese category of the BMI.