It sounds like this is a banquet type venue. Is evryone eating at the same time? If so, and your show is BEFORE the meal, ask the kitchen staff what time they plan on serving the meal. They can probably give you a time frame. As for your case, keep it in a secure location but where you can still have access to it.
Thanks michal, i just called him up and asked him a few quesitons its, booked for the 22nd of Feburary, Sunday. From what he told me he is arriving at the restruant at 11:30 and wants me to ocme entertain at 1:30 which give them about a 2 hour time frame to eat, and it is a banquet like you said. Which is good, well better than i thought.
About the case. . . should i just pop it on a tray jack (keyboard stand) and put it in the corner or would that be bad for my and the restruants image?