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

       /INTERVAL=seconds

    Specifies the number of seconds that display information remains
    on the screen before it is updated. By default, the interval time
    is 15 seconds.

    If you use an initialization file in noncontinuous mode and the
    initialization file contains a SET SCREEN command that changes
    the screen size, SHOW CLUSTER sets the screen to the specified
    size for one update interval and then sets the screen to the
    original size.