1st time at the track advice.
If you want to just get a feel for things the first time around, and a time on your car, "don't fight" with the tree. The timer starts WHEN YOUR TIRES LEAVE the lights, and have nothing to do with the green.
So if you want to concentrate on launch, don't get all rattled with the yellows and green. Just take your time, and LAUNCH It won't matter if you set there on the green for 5 seconds, although some of the "crowd" might wonder.