Gnash has three time implementations: one using boost::date_time, which handles portability itself, one for POSIX systems and one for Win32.
Namespace clocktime contains a unified source for wall clock time: this is used mainly for the timing of movie advances and in the ActionScript Date class. FPS profiling also uses clocktime:: for a relatively high resolution, robust timer.
The boost::date_time has the great advantage of handling portability itself, as well as being able to handle a much larger range of true dates. Its disadvantage is that date_time requires not only header files, but also a run-time library, and thus increases the requirements.