FFF
There are 24 time zones. 25 letters are used as the time zone that straddles the International Date Line is known as either 'M' or 'Y' depending I suppose whether you are reckoning +12 from Zulu time or -12. Letter J is not used.
Offset 30 minute times are used in India and in Central Australia probably other places, but there is not a specific identity for these.