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

    TIMVCFAIL specifies the time required for an adapter or virtual
    circuit failure to be detected. Compaq recommends that the
    default value be used. Compaq also recommends that this value
    be lowered only in OpenVMS Cluster of three CPUs or less, that
    the same value be used on each computer in the cluster, and that
    dedicated LAN segments be used for cluster I/O.

    TIMVCFAIL is a DYNAMIC parameter.