Each time the - n flag appears, that network name is added to a list of valid networks. All other networks are ignored. Each time the - i flag appears, that network name is added to a list of networks to ignore. All other networks are used by the time daemon. One way to synchronize a group of machines is to use an NTP daemon to synchronize the clock of one machine to a distant standard or a radio receiver and - F hostname to tell its timed daemon to trust only itself.
Messages printed by the kernel on the system console occur with interrupts disabled.
This means that the clock stops while they are printing. A machine with many disk or network hardware problems and consequent messages cannot keep good time by itself. Each message typically causes the clock to lose a dozen milliseconds. A time daemon can correct the result. If two or more time daemons, whether timed or ntp, try to adjust the same clock, temporal chaos will result.