Yealink SIP-T54S Administrator's Manual page 284

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
Parameters
and "YY" represents a two-digit year. The value configured by the parameter
"lcl.datetime.date.format" takes precedence over that configured by this parameter.
Web User Interface:
Settings->Time & Date->Date Format
Phone User Interface:
Menu->Basic->Time & Date->Time & Date Format->Date Format
lcl.datetime.date.format
Description:
Configures the format of date string.
Y = year, M = month, D = day, W = day of week
Value formats are:
Any combination of W, M, D and the separator (e.g., space, dash, slash).

Example:
lcl.datetime.date.format = W,MD
The IP phone will display the date in "W,MD" format (e.g., Wed,0420).
Any combination of Y, M, D, W and the separator (e.g., space, dash, slash).

Example:
lcl.datetime.date.format = YYYY-MMM-DDD-WWW
The IP phone will display the date in "YYYY-MMM-DDD-WWW" format (e.g., 2016-
Apr-20-Wednesday).
Note: "Y"/"YY" represents a two-digit year, more than two "Y" letters (e.g., YYYY) represent a
four-digit year, "M"/"MM" represents a two-digit month, "MMM" represents the
abbreviation of the month, three or more than three "M" letters (e.g., MMM) represent the
long format of the month, one or more than one "D" (e.g., DDD) represents a two-digit day,
"W"/"WW" represents the abbreviation of the day of week, three or more three "W" letters
(e.g., WWW) represent the long format of the day of week.
Web User Interface:
None
Phone User Interface:
None
To configure the time and date manually via web user interface:
Click on Settings->Time & Date.
1.
Select Enabled from the pull-down list of Manual Time.
2.
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Permitted Values
String
Default
Blank