You know these things because you can translate one local time to UTC then from UTC to the other local time if you are given the UTC offsets. Why not skip two steps and just have everything UTC to begin with? You can establish that the NYC folks work from 1300 UTC to 2200 UTC, and the UK folks from 0800 UTC to 1700 UTC. So it's trivially obvious that meetings between 1300 and 1700 UTC will fall within everybody's working hours.
So what about some place you are not familiar with? Let's pick Hong Kong. You would indeed need to contact them for their exact work hours. (Heck, maybe they work nights so that they can be awake during US or UK working hours because that's where their customers are; you just don't know.) Or, the +1, -8, +10 time zone designations could be retained to indicate how much time passes between noon in Greenwich and noon locally, yet still all local clocks and global coordination be done in UTC. But that still doesn't give you all the info you need - all of China, for example, is one time zone but I have absolutely no clue if 8 am to 5pm China time is standardized across the entire nation - 8 am in Hong Kong is astronomically like 4 or 5 am in western China - do they work 8 am to 5 pm China time, or do they work 12 pm to 8pm China time?
Isn't that how aviation and the military do it? Zulu time? Even when they're in a location where 0000 Zulu means is bight and sunny, so as to not cause confusion when talking to a location that might or might not be one two, or twelve time zones away? Heck, even two different locations at the exact same latitude could be in different time zones so even though the sun is at the exact same location in the sky for them, one is an hour ahead of the other. It'd be so much easier to just dispense with translating between time zones and all use a common cock.
Well, it's 23:03 UTC right now, time for me to finish my comment. (I have a UTC clock set up to display on my computer.)