[harshreality]

You can't figure that by stepping outside, because even today local timezones do not make breakfast/lunch/dinner/sleep/wake times constant across different timezones or cultures. When you travel to a new place in an all-UTC world, you'd note the local typical work hours, meal times, socialization time, and night time just as you would now. It's up to you how closely you adhere to those norms, depending on your work and social habits.

The logical extreme of local timezones is to have your gps-equipped mobile automatically adjust the time so that the sun is highest in the sky at or shortly after noon. Of course, that would create chaos.