You can compare longitudes within a timezone. China is on one big timezone, and if you're out in Xinjiang "8am" means something totally different from in Beijing. I live in Chicago, which is about as far east as Central Time goes. You could compare to western Kansas. If one of us is "daylight time" by the sun, the other is "standard time", more or less. Or hell, about an hour straight south of me (Indianapolis) it's on Eastern time. Same longitude, same latitude, but one city is ET and one is CT. There's a comparison to look at as well.