I remember read that time zones was created due to railroads and telegraph line because now you could be on the other side of the country almost the same day plus the messages moved faster than the earth turning and I guess that +12 and -12 because the day has 24 hours.

By the way I read now that you mention this, a proposal from two guys to destroy the whole system because it became obsolete for internet, so maybe China had a vision of the future.