"Begin moving your foot and your body forward. . For every 2- 3 inches the foot is in motion count 1 2 3. See if you can get to all the way to 10 before the foot takes weight and has to stop moving. There is one stipulation though. You cannot count if the foot is moving by its self. Your count must start when the body starts moving forward and must stop when the foot takes weight. The test is how long can you keep your moving foot in motion."
It you obey the stipulation - which is to say, if you keep your body moving, it will soon be projecting into imbalance because it will soon have travelled quite a bit more than the short length of the standing foot. The degree to which you can keep the step going, and avoid landing on the moving foot sooner than intended, then depends on three things;
1) How much you drive from the standing leg. Drive can keep your body up (or at least upright in a good vertical posture), though only in concert with accelerating your movement, because you are supporting the body in an unbalanced position.
2) How strong your standing toes are. The stronger your toes, the more forward in your foot you can put your point of support, and thus the more you can move your body forwards before you even start to go off balance.
3) How LATE you bring your moving foot through. The moving leg weighs quite a bit. Even with the foot on the floor, having it out in front of your body would cause you to go into imablance sooner. But if it does not pass your body until the movement is well established, you can delay the point when the leg itself causes you to have to put weight on it.
It should be noted that a lot of students first given such an exercise will hold their hips back to retain balance as they "move" their shoulders forward, and claim that this contstitutes moving their body. Given how horrible such hunching forwards makes things for a partner, it's clear that it doesn't. To be moving, you must be moving your hips and center, and that will very soon mean that they are no longer over your standing foot. It's the ability to keep extending a step after it reaches the point of imblance which seperates the large and full travel of champions from more casual dancers.