Its right next to the Innoventions building. As you enter Tomorrowland, go past the Orbiters, past Star Tours, around the old PeopleMover/Rocket Rods platform and you'll see it straight ahead, slightly to the left.
You don't have to make a mad dash unless maybe you are trying to get the tour on a weekend. We got there about 10:30 on a Thursday morning last week when the park opened at 9, and each tour was only about 1/3 full.