Correct. But since we know that Mahmood used RS-422 and ethernet cables, we know that the state of Internet in Jordan would be irrelevant. In this case, the clocks are quite close together - within the distance you can span with RS-422. So there are no big and unknown ping time between master and slave to take care of. The delay is the baudrate delay and the delay from the code filling the transmitter and the code picking up data from the receiver.

So the NTP protocol would not have given an advantage.

And the use of real Ethernet would have added extra costs compared to the RS-422 driver.

The more interesting alternative would have been to consider ZigBee Pro, or similar, to potentially pay for for the electronics but instead reduce the cost of drawing the wiring. But that would depend on the availability to power close to the clocks, making it significantly cheaper to draw power wires than to draw the Ethernet wires all the way to the master unit.

Edit: Or as an alternative have all slaves just contain a GPS as time reference - but that would add some extra troubles with daylight savings.