When replacing batteries...
Leave the batteries out of the clock for at least ten seconds before inserting new batteries. Follow one of the three methods below.
Install the clock's batteries between 39 minutes past the hour and 6 minutes after the next hour. It should set the time right away if it's near a transmitter.
Install the batteries at any time of the day. The clock will set its time at the next 39 minutes after the hour.
Power cycle the nearest transmitter. It will then broadcast for 8 consecutive hours and clocks will set immediately on power-up.
More detailed, and confusing, information about the Primex clocks can be found at https://support.primexinc.com/hc/en-us/articles/360022647393-Analog-Clock-setup