If you’re talking about how long you should wait to eat after working out, you want to eat pretty much as soon as you catch your breath.
Your body goes into a kind of “debt” after you work out where your blood sugar is depleted and needs to be replenished. This is why you’re usually pretty hungry once your pulse calms down a bit. When your body is in this state, it is primed to store food as glycogen in your muscles instead of as fat on the backs of your thighs.
This window of good times lasts about an hour after you exercise, and you want to take full advantage of it.
If you’re talking about how early you should eat before working out, that’s something you’re going to have to figure out for yourself. Every meal is different and every body is different, but here’s your rule of thumb: You should eat early enough (and intelligently enough in terms of what you eat) to be pretty sure that you’re not going to throw up once you get moving, but not so early that you’re hungry again once you break a sweat. Make sense?