A method for dynamically reconfiguring time zones in real-time using plural time zone (TZ) libraries is provided. The method provides integrating a first time zone information data (TZID) version and a second TZID version into a TZ library in an operating system. A first configuration comprising the TZ library and the first TZID version is selected. Responsive to adjusting the first configuration to a second configuration comprising the TZ library and the second TZID version, the second configuration is used automatically without restarting the operating system and without restarting an application.