VMS Help MONITOR, MONITOR, Command Qualifier Descriptions, /BEGINNING  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BEGINNING=time

    Specifies the time that monitoring begins, by using a combination
    of absolute and delta times. Observe the syntax rules for time
    values described in the online help topic DCL_Tips (subtopic
    Date_Time).