To give you an idea, the last time we went, our party split up right before fireworks. 2 of us went to TT single rider, the rest went to Frozen. Both lines were listed at an hour but were quickly dwindling. The TT riders finished the ride, then went over and did Frozen too. we were only about 10 minutes behind the group that went straight to Frozen when we got off. 6 split 3-3 is a strange number of passengers. Groups of 4 usually want to be split up 2 and 2, not 3-1 with a separate couple. LOTS of cars end up partially filled so single riders get on pretty quickly.
Funny story - a LONG time ago my wife and I tried all week to ride the original TT. It kept breaking down, getting shut down by lightning, or the line was just plain too long. We finally did single rider and both got on, with my wife one car ahead of me. I got off and couldn't find her anywhere. The thing is on a fixed track, how could she get lost? Turns out the car she got on got a flat tire and was automatically taken back stage. they walked the group around backstage and put them on another car.