Library /sys$common/syshlp/nclhelp.hlb set, modem_connect, line, transmit_holdoff_timer  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: 0

    Necessary delay, in milliseconds, between the transmitter
    being disabled and being enabled again. The value 0 means
    that the request to send signal can be asserted as soon as the
    client requests it. This characteristic is not supported if the
    characteristic modem control is none.