Show HN: Seven39, a social media app that is only open for 3 hours every evening

It's an interesting idea, but if it's only open at a convenient time for a particular group, it's going to lack diverse and worldwide perspectives, and those are important for building a welcoming ecosystem. I doubt giving each timezone its own 3 hours would work, but perhaps rotating the 3 hours each day so that it's anchored on a different timezone would encourage that diversity of content and perhaps even encourage creating connections across timezones.

That said, if you've had success with it in a friend group, perhaps that suggests it's a nice mechanism for a group chat app, rather than for a public social media site?

Name a social media site that has diverse and worldwide perspectives that also feels welcoming.

Quite the contrary. Welcoming ecosystems are discriminatory because necessarily exclude those who generally aren’t interested, or act in bad faith.

Community is local.