I will grant this though, if one wanted to say that there are only 24 time zones on earth then I can see how one could say this from a mathematical perspective (solar time). In 24 hours the Earth rotates through 360 degrees with respect to the Sun, for every 15 degrees east or west of the Greenwich meridian you would reach a different time zone (or solar time if you will). For that reason I would be fine with somebody saying the answer is 24. But that has nothing to do with the human construct of adding or subtracting an hour/half hour/etc. in an area they live in.
So if anybody wants to say the answer is 24, I am fine with that, math wise that answer is correct.
27 is not correct no matter how you look at it.