This doesn't square with my perception of SV programmers always mentioning staying late to hack on their startup. Do they actually mean that they got there at 6AM, so staying until 5PM is "late?"

Engineers might stay up until 2am, but they stay up until 2am at home because nobody else is bugging them. If they eat, it's gonna be cheap stuff or frozen trader joes food from the freezer, more time efficient.

I don't think that it's all hackers. Without mentioning the neighborhood (because this borders on stereotype, and these things usually devolve into an x vs. x neighborhood discussion), I live in a neighborhood where people mostly hold non-technical titles like "marketing manager" and "product manager".

And they've all worked out, shopped for groceries, had breakfast, etc. before 9am.