If you check in early on Sunday your voice will be gone that much sooner!!!
Definately wait as long as you can before checking in on sunday. Since chow is one of the worst places to be at OCS, if I were you I would hang out with in the OCS area and observe what is going on without being too obvious or letting on you are there for OCS...then watch your class mates go to chow for lunch...check in after they are done eating. My recommendation is to check in anytime after they go to lunch and before they go to dinner.
Here is a tip for the chow hall....forks are to the left, spoons in the middle, knives are on the right....you will understand when you get to chow...those who have been there know what I mean.
Also, if you want to make life really easy and interesting...empty a tube of toothpaste about halfway...then fill it with amonia and top of the tube with by squirting some toothpaste in from another tube. In the middle of the night go to the head and stop up a sink....then soak your belt buckles in the amonia for about 3 minutes, any longer will discolor the brass. The amonia will remove the micro thin plastic coating on the belt buckles they give you. The bulk of your time during poopy week is spent standing around polishing the plastic film off the buckle and it muse be completely off your display buckle and the buckle you wear during your inspections. I think they take away bottles of mouthwash, that is why I recommend the toothpaste tube.