A central time-of-day reference is integrated into a switch which interconnects I/O devices and host processors in a computer complex via fiber-optic links. A time reference oscillator in the switch serves to generate incrementing reference signals for the central reference and also provides a clock signal for the switch transmissions. Units to which the switch is attached obtain clock signals from their regenerated clocks which are synchronized to the time reference oscillator, and use the regenerated clock signals to control their local time-of-day references. Each unit periodically transmits a signal to the switch requesting a dynamic connection to the switch-based central time-of-day reference in order to receive a time of day message.