Get a ride next time at the next event with an instructor and see when he/she blips the throttle in relation to the braking zone.
This is a post I made LONG long time ago to help people visualize the actual heel-toe maneuver and just about how quickly it happens:
Originally Posted by The HACK
Here's a couple of diagrams I made, originally intended for class-room sessions at some of the schools we teach...
This is the "traditional" definition of a heel-toe. Heel of the foot on the gas, toe of the foot on the brake. The position of the car in diagram indicate how quickly and how short of a distance you typically have to get this accomplished.
This is the alternative way I was taught, it's especially effective on cars where the pedals are close, or for guys with repeated ankle sprains/injuries where rotating the foot in via a traditional sense of heel-toe becomes increasingly difficult with age. Keep left side of the ball of your foot on the brake, rotate your whole foot to the right to catch the gas pedal with the right side of your foot. Takes some practice, but it comes easier for me on a BMW.
On cars like a Nissan 350Z, where the gas and brake pedals are far apart and meant for a traditional heel-toe, since I don't have a lot of flexibility in my ankle anymore, I rotate my foot the OTHER WAY and catch the brake pedal with the ball of my foot on the right, and rotate my foot forward and catch the gas pedal with the tip of my toe. Works just as well.
Which way you "heel-toe" also "hinges" on how the gas pedal is attached, I've found.