Start stop saves fuel if the engine is off more than seven seconds. It wastes fuel any time less than seven seconds. On my VW and Jeep I hit the off button before I back out of the garage. In my case I’m definitely saving fuel by doing this as I seldom run into traffic that would stop me more than seven seconds. Additionally in the VW mine doesn’t activate unless I put decent pressure on it. Braking just enough to keep it from rolling forward and it rarely engages.
Here is EE’s video on the topic.
Here is EE’s video on the topic.