For the purposes of this market, a time zone is defined by a number of hours offset from UTC, eg. UTC+2. As long as at least one country uses a particular offset, that offset is included in the total number of time zones.

Time zones that change offsets during the year (due to DST/Summer Time) will be counted by the offset used during Standard time; hence each time zone can be counted at most once.

Currently, there are 38 different offsets from UTC used around the globe.

https://en.wikipedia.org/wiki/Time_zone

The market will resolve when the number of offsets listed on the above wikipedia page changes to something other than 38.

ADDITIONAL INFO:

As best I can tell, the most recent change to the number of time zones was in 2015, when Norfolk Island (Australia) switched from UTC+11:30 to UTC+11:00. As this was the only area using UTC+11:30, the number of time zones was thereby decreased by one.

Similarly, the most recent increase in the number of time zones was in 1994, when the island nation of Kiribati switched its eastern half to UTC+13:00 and UTC+14:00, which were previously not in use.