24 time zones on earth, though

Even if you just count UTC offsets, there's 38 time zones: https://en.m.wikipedia.org/wiki/Time_zone

There's more than that though, due to Daylight Saving Time. The rules for DST are part of the definition of the time zone. For example, in Australia, Queensland and Victoria are both UTC+10. However, Victoria observes DST while Queensland doesn't, so technically they're two separate timezones (in the Olsen database, they're Australia/Melbourne and Australia/Brisbane respectively).