/sys$common/syshlp/helplib.hlb CC, Run-time functions, difftime  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Computes the difference, in seconds, between the two times
  specified by the time1 and time2 arguments.

  Syntax:

       #include <time.h>

       double difftime (time_t time2, time_t time_1);