Multiplicity of time standards

The world was previously divided into 24 time zones based on 24 standard meridians 15 degrees apart in longitude, starting at Greenwich (UK). However, these theoretical divisions cut across states and divided adjacent areas inconveniently, so the division has therefore been considerably modified in practice. This modification has been carried further by the adoption (from time to time in different countries and at different times of the year) of summer-time or daylight saving measures. These time differences create considerable difficulty in setting up international timetables and maintaining time-based historical records. The multiplicity of time standards increases the difficulty of conducting international business, because of the limited overlap in working hours in different time zones. Some world-wide organizations are able to exploit these difficulties to their own advantage.
(F) Fuzzy exceptional problems