Yealink SIP-T54S Administrator's Manual page 289

Parameters
Description:
Configures the offset time (in minutes) of Daylight Saving Time (DST).
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->Offset(minutes)
Phone User Interface:
None
To configure the DST via web user interface:
Click on Settings->Time & Date.
1.
Select Disabled from the pull-down list of Manual Time.
2.
Select the desired time zone from the pull-down list of Time Zone.
3.
Enter the domain name or IP address in the Primary Server and Secondary Server field
4.
respectively.
Enter the desired time interval in the Update Interval (15~86400s) field.
5.
Mark the Enabled radio box in the Daylight Saving Time field.
6.
- Mark the DST by Date radio box in the Fixed Type field.
Enter the starting time in the Start Date field.
Enter the ending time in the End Date field.
- Mark the DST by Week radio box in the Fixed Type field.
Configuring Basic Features
Permitted Values Default
263