1/1000000 of the fundamental unit of time in the Furlong/Firkin/Fortnight system of measurement; 1.2096 sec. (A furlong is 1/8th of a mile; a firkin is 9 imperial gallons; the mass unit of the system is taken to be a firkin of water). The VMS operating system has a lot of tuning parameters that you can set with the SYSGEN utility, and one of these is TIMEPROMPTWAIT, the time the system will wait for an operator to set the correct date and time at boot if it realizes that the current value is bogus. This time is specified in microfortnights!
Multiple uses of the millifortnight (about 20 minutes) and nanofortnight have also been reported.