I work in fast food, Hardee's actually. Depending on what makes the resturant famous (like a certain burger, or maybe the breakfast, etc) depends on the time it gets the most action.
We get more for breakfast then anything, but if you only include dinner, about 12 to 2 or 3 is the time we get the most buisness.
From my experience, customers tend to come in during lunch the most. Ranging from 10:45 to about 1:00. Lunch rush hour is the worst. It can be different on weekends depending on the location of the restaurant. On weekends it can be busy both breakfast and lunch hour.