Trying the green light chime this morning. I think it worked like 8 out of 10 times. A couple of times, light turned green even on my screen but without the chime.
The chime will not sound if you begin to move first. In manual driving, this means if you press the accelerator even slightly. In TACC or Autosteer, if you click the stalk down to re-engage or confirm as a lead car before the chime, it won't sound.
I'm still trying to understand exactly how the new feature is supposed to work when you're not the lead car. It's clear that in the prior FSD-only feature Traffic Light and Stop Sign Control, no chime will sound for a green light when you are not the lead car, because in that case the car would decide to move forward on its own and no chime is needed.
But in using the Green Light Chime in manual driving, I think it doesn't sound when you have a lead car in front of you that hasn't started to move yet after the light turns green. This is good behavior because there's a danger that drivers will incorrectly train themselves to press the accelerator, immediately and almost unconsciously, as soon as the chime sounds.
So it's better if the chime sounds only when there is both a green light and
no lead car still waiting directly in front of you. When a waiting lead car begins to move, the held-off chime will then sound to alert you, but if you've already started to move within about one second, it will be canceled and you'll never hear it.