The wait time just depends, if the park is really crowded the train station is usually really crowded. If the train just pulled away when you walk up you have to wait for the next train. They will run several trains though when the park is crowded.
The train circles the park, stopping in Toon Town, the Main Street station, and Adventureland, so, the ride is as long as you want it to be. You can do the entire circle or get off at another station, using the train for transportation, which is what we did a couple of weeks ago.