You change the time in the phone system that the ETR-18D phone is connected to.
If you are connected to a Merlin Legend or Merlin Magix, you go to the programming console phone, press
Menu
System Program
Exit (or Start)
System
Time
(If you get a choice of System Time and ADST, pick System Time)
Backspace out the current time
Dial the correct time, military format
Enter
Exit (or Home)
Now, if that ETR-18D phone is actually connected to a Partner system, and just has the wrong designation strip installed on it, go to Ext. 10 and press:
Feature 00
Left Intercom twice
#103
Dial the correct time in military format
Feature 00
Good luck!!