No need to excuse yourself from a summer barbeque to feed the horses at a specific time. A ration delivered a few hours earlier or later won't harm a pleasure horse or one in light work. If anything, varying the schedule may help prevent anticipatory behaviors such as pacing and stall kicking.
One key to feeding flexibility is to offer free-choice hay and then enough grain to maintain a horse's condition divided into as many meals a day as possible. Chowing down a heaping serving of starchy grain on an empty stomach can lead to laminitis or colic.
An elite athlete, however, needs to eat on a more rigid schedule. Every calorie he consumes is precious, and a regimen that delivers meals at the same hour each day—give or take 30 minutes—optimizes digestion so he extracts every bit of energy from his grain.