/sys$common/syshlp/helplib.hlb SET, DEVICE, Qualifiers, /MVTIMEOUT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /MVTIMEOUT=n DSAnnnn:

    Specifies the mount verification timeout value to be used for
    this shadow set, specified by its virtual unit name, DSAnnnn:.

    The value supplied by this qualifier overrides the system
    parameter, MVTIMEOUT, for this specific shadow set.

    The valid range for n is 1 to 16,777,215 seconds.

    The device specified must be a shadow set that is mounted on the
    node where the command is issued.