As an academic, I used to work 11am-8pm many days when I was younger thanks to flexible working hours, and I wasn’t the only one working late but not early. I realize this is probably more rare in corporate settings, but keep in mind if the place has flexible hours you might see more people at 6pm despite people not doing 996.
What i'd assess at 6:30 is whether people are on meetings or on focus time. If you have monitors with zooms full of 5-6 people, I wouldn't think that is flex hours, i'd assume that is a meeting being scheduled at 6:30.
On the other hand, if you have people focus working, you cannot draw any conclusions from that.
Personally, I stay at work late. But there is a difference between me being obsessed with a problem and working thru the evening trying to solve it (awesome for me) vs meetings that are being scheduled at 6:30pm or 7pm
I have a very tough time in the morning convincing myself to go to work, and a very tough time at work tearing myself away from something in an intermediate state. Things at work are always in an intermediate state at 5:00, unless you stopped working well before then (or got very lucky), so I always end up working late whether I come in on time or come in late.
So I'm always trying to get to the point where management lets me get there when I get there, and trusts me to be productive. It's a mental thing. I get up early and do a lot in the morning; I'm a morning person. Maybe too much so. The time between getting off work and going to bed is garbage time for me; a long annoying commute and a meal. When I leave at 5:00 I just fall asleep by 9:00.
Nobody wants a "visit" from the founder, anyway. They want timely two-way flow of information, access and guidance on the occasions when they need it, and maybe (maybe) an occasional chance to hang out socially as a group with no reference to work. Nobody wants the founder randomly dropping by during work hours to assess morale.