Paul Clip was inspired by my novel Eastern Standard Tribe and made a set of analyses of world population by timezone.
I cheated a little by using a simplifying assumption: if a country has multiple time zones, I divide its population evenly between them. This inaccuracy doesn't change the fact that our top three are...
UTC+8: China and others
UTC+5.5: India and others
UTC+1: Western Europe and a good chunk of Africa
According to Mathematica, there are 39 different time zones ranging from UTC-11.5 to UTC+14. I wonder if anyone has visited them all? Now that would be a glorious adventure!