My race day breakfast usually consists of cereal, coffee and toast. And I usually try to eat that at least three hours in advance of the start of the race. But find out what's best for you. Experiment in the months and weeks leading up to the race. Find out what you're comfortable with.
Some people can run an hour after eating.
Others need four hours. We're all different. There's conflicting views about what's necessary and much depends, once again, on what suits each individual. For most races, other than marathons, I prefer to jog easily for around 15 minutes - or perhaps longer if I've undertaken a lengthy journey cramped up in a car, bus or train. After that a few strides, no more than 100m each, helps stretch out the legs.