Is Tokyo in the some timezone as Beijing? Is London in the same timezone as Reykjavik? Did Mexico start daylight savings last week or now? I have to look up stuff to answer these things, as well as the local timezone designation (is it ET or EDT? Is it CT stand for "california time" or CT for "central time"? Is there a CT in another part of the world that could be misunderstood by another participant?), so that I can publish the meeting time correctly without people misunderstanding it. Roughly avoiding unreasonable times is much easier to do than this. The sleep times of Reykjavik and the sleep times of London don't really differ by much, so as long as the proposed time steers clear of that, it will be fine.

In fact all I need is a world map that shows me the day/night part of the Earth as I slide the (UTC) time -- there are many apps that do this already. Then schedule the meeting such that the greatest number of participants fall under the daylight. Then publish the meeting as a single UTC time. That's it.