Seems like he's always considered this a good measure of a founder's quality.
From a 2019 interview- https://conversationswithtyler.com/episodes/sam-altman/
> You know, years ago I wrote a little program to look at this, like how quickly our best founders — the founders that run billion-plus companies — answer my emails versus our bad founders. I don’t remember the exact data, but it was mind-blowingly different. It was a difference of minutes versus days on average response times