Panasonic KX-T123211D
  1. Use phone with intercom number 101 (probably the receptionist's phone). It will change the time for all phones. 
  2. Move MEMORY switch on back of that phone to PROGRAM. 
  3. Keep handset down and press 0 on touch-tone dial. 
  4. Dial year with two digits (e.g. 97 for 1997). 
  5. Dial month with two digits (e.g. 01 for January). 
  6. Dial date with two digits (e.g. 03 if today is the third day of the month). 
  7. Dial day with one digit (1 for Monday, 2 for Tuesday, 3 for Wednesday, 4 for Thursday, 5 for Friday, 6 for Saturday, 0 for Sunday). 
  8. Dial hour with two digits (i.e. 01 for 1 o'clock). 
  9. Dial minutes with two digits (i.e. 07 for 7 minutes). 
  10. Dial 0 for AM, or 1 for PM 
  11. Press either AUTO DIAL/STORE or AUTO/MEMORY, depending on your phone. 
  12. Move MEMORY switch on back of phone to SET.