I'll update this if I find more. For now, this seems to be a partial solution. It's a Gmail add on (except I don't use Gmail) that adds reminders. The options when setting reminders include cancelling it if someone replies, and to remind everyone in the thread. If you combine those two, it seems like — if you use Gmail's web client and have $23/month you're dying to get rid of — a decent way to add the feature. Source: over 1 year ago

Moment-timezone is pretty great. However the moment library is no longer maintained, and there's some complications to its use due to it being mutable. Still works great though. Source: over 1 year ago

It was actually much easier to make than I thought it would be, thanks to Moment. - Source: dev.to / almost 2 years ago

The clock is in Javascript. Time zones in JavaScript historically are non-trivial since everything is based on the client clocktime. Fortunately, there is moment.js and moment-timezone-with-data.js that vastly simplify getting the current time at the NYSE. The clock keeps ticking correctly irregardless of which tab is active. I find the clock to be also functional since the WSBoy is worn over where I would... Source: over 2 years ago

I used the Moment-Timezone library, which returns, well, all the timezones! Super easy to get started with, just add using npm or yarn to add it, and then add import moment from 'moment-timezone'; to the top of your file. - Source: dev.to / over 2 years ago