I'd argue that an open office, in the absence of strict library rules, is analogous to an all-day meeting, e.g. "quick question!".
Meekan looks interesting, and they have the idea right (since as a third-party they are limited), but it's a plugin, and it's a bot[1]. Scheduling would be a core concept of my theoretical group-chat app - something you were incredibly encouraged to do by the interface, instead of bothering an arbitrary number of people that are probably trying to focus.
[1] the problem with bots is that it pushes stuff that ought to be "interface" into public view, with all of the notification and visual noise baggage that is implied by that.
Date/time localization should just work, here Amy needs to manually ask for it, and everyone else is notified that she did! And that doesn't even cover language localization! If I'm having a meeting with a colleague whose English is weak and prefers Chinese, will it just drop even more noise into the chat when she requests a translation?