DKT-2020 Corded Phone (dkt2020sd): How do you change the display time on the DKT2020-...

Depending on the type of system you have powering the 2020,this should take care of it.
Leave the handset on hook, press intercom # 6 5 2, then enter the time of a 24 hour clock, entering 2 digits for the hour, 2 digits for the minutes, and 2 digits for the seconds – enter a leading 0 for any single digit entered,
press Redial,
press Speaker.
This must be done at extension 200 – usually the receptionist phone.
For example, if the time is 2:15 P.M., press intercom # 6 5 2, 1 4 1 5 0 0, Redial Speaker