This post is related to my discovery of differences in behavior between posix_time::from_ftime and C# DateTime.FromFileTime methods (earlier post) Now I am trying to learn the proper usage of posix_time and time_zones. After reading the documentation I am still confused regarding usage of the timezone together with usage of classes/functions in posix_time namespace Is it possible to do smth.like this: First declare the time zone, like EST, CT ets and then all subsequent calls to posix_time namespace functions or classes will take this timezone as a base? I will really appreciate a simple example of specifying EST timezone for posix_time.