Hint: Daylight Saving time does not exist in Antarctica.
Some zones north-south of each other in the mid Pacific differ by 24 hours in time: they have the same time of day but differ by a full day. The two extreme time zones on Earth (both in the mid Pacific) differ by 26 hours. A particular day starts earlier in countries with a more positive UTC offset. Thus the first occurrence of a date will be in UTC+14 and the last of the same date in UTC−12. This gives the interesting feature that during one hour each day there are three different dates in use on land around the world, at 10:30 UTC Monday it is already 00:30 Tuesday in the Line Islands (UTC+14) while the time is 23:30 Sunday in Samoa (UTC-11).
All of China (which should span five time zones) uses a single time zone.