VMS Help Sys Parameters, GLX_INST_TMO_  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    (Alpha Galaxy platforms only) GLX_INST_TMO is the time (in
    milliseconds) that an instance in a Galaxy sharing set can fail
    to increment its timeout value before the other sharing instances
    presume that the instance failed and remove it from the sharing
    set.

    The default is 20,000 milliseconds (20 seconds).