Valtteri Bottas's not-a-jump-start was the biggest talking point after the Austrian Grand Prix, certainly for Sebastian Vettel. But he did nothing wrong and the others were asleep, so his rivals should get over it.
The speed of light is almost 300 million metres per second. The lights are, by definition, a light source and the distance from the front of the grid to the back could be around 200 metres or so. In reality, that means zero difference in time, so it is all about human reactions.
The teams will (or should) have supplied each of their drivers with a startline simulation light box kit. They should have this at home to practice their reactions to the lights going out. It will function exactly the same as the real thing, the only difference being the lower stress level of your lounge compared with that of the F1 grid.