What you’re describing is LITERALLY the system we have. UTC is a global, coordinated time that tracks solar time to a precision of less than a second. As far as my computer is concerned, my time is UTC (technically GMT, but they both refer to the same time) minus 6 hours. We all could choose to say, “hey, wanna meet for dinner at 3AM?” and have that be a normal thing to say in my area, and an odd thing to say odd in Europe… but nobody wants that.