Note: Change the clock from the attendant's station -- usually extension 10, 100, or the first extension in the extension number range (i.e., 200 for 200 to 299 range , etc.) -- with handset resting on the cradle and the phone not in use.
Press SPEAKER button
Dial 728
Dial
two digits for the hour (24 hour clock, 13 = 1:00 PM)
Dial
two digits for the minutes (00 thru 59)
Press SPEAKER to exit