Library /sys$common/syshlp/ncphelp.hlb SET, LINE, VALID TRANSMISSION TIME microseconds  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies only to FDDI lines.  Specifies the maximum time between
 arrivals of a valid frame or unrestricted token.  Microseconds must
 be a decimal integer in the range of 2500 to 5222.  The default
 is 2621 microseconds.