I believe EVERY retaurant has happy hour. Hours vary, with NASCAR Cafe having the most generous hours (if memory serves). generally, figure 4 to 6 or 5 to 7.
There was an extensive discussion of happy hour here a while back. Maybe someone more technically savvy than I can post a link to that thread.
Happy hour IOA:Enchanted Oak Tavern - 3-6pm
Backwater Bar - 3-5(?) Pm
US:Finnagans - 3-5(?)LA BAmba - 3-5(?)The best kept secret:Alcatraz - 2-5(?)
And don't forget City Walk has happy hour until7
hope that helps