Yealink SIP-T54S Administrator's Manual page 288

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
Parameters
local_time.start_time = 1/1/7/0
Note: It works only if the value of the parameter "local_time.summer_time" is set to 1
(Enabled).
Web User Interface:
Settings->Time & Date->Start Date
Phone User Interface:
None
local_time.end_time
Description:
Configures the ending time of the Daylight Saving Time (DST).
Value formats are:
Month/Day/Hour (for DST by Date)

Month/Week of Month/Day of Week/Hour of Day (for DST by Week)

If "local_time.dst_time_type" is set to 0 (DST by Date), use the mapping:
Month: 1=January, 2=February,..., 12=December
Day: 1=the first day in a month,..., 31= the last day in a month
Hour: 0=0am, 1=1am,..., 23=11pm
Example:
local_time.start_time = 12/12/22
If "local_time.dst_time_type" is set to 1 (DST by Week), use the mapping:
Month: 1=January, 2=February,..., 12=December
Week of Month: 1=the first week in a month,..., 5=the last week in a month
Day of Week: 1=Monday, 2=Tuesday,..., 7=Sunday
Hour of Day: 0=0am, 1=1am,..., 23=11pm
Example:
local_time.start_time = 4/3/2/3
Note: It works only if the value of the parameter "local_time.summer_time" is set to 1
(Enabled).
Web User Interface:
Settings->Time & Date->End Date
Phone User Interface:
None
local_time.offset_time
262
Permitted Values
Time
Integer from -300 to 300
Default
12/31/23
Blank