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

    Default: 1000

    Minimum timer, in milliseconds, that the DTE will deassert data
    terminal ready during a disconnection. This characteristic is not
    supported if the characteristic modem control is none.