VMS Help BACKUP Command, Qualifiers, /BEFORE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BEFORE=time

    Input File-Selection Qualifier

    Selects files dated earlier than the date and time you specify.

    Specify the date and time as a delta time or as an absolute time
    using the format [dd-mmm-yyyy[:]][hh:mm:ss.cc]. You can also use
    one of the following reserved words to specify the date and time:

    BACKUP     The BACKUP date of the file written by a previous
               BACKUP/RECORD operation (available only on Files-11
               Structure Levels 2 or 5 volumes)
    TODAY      The current day, month, and year at 00:00:00.0 o'clock
    TOMORROW   24 hours after midnight last night
    YESTERDAY  24 hours before midnight last night