Yealink SIP-T54S Administrator's Manual page 278

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
Parameters
local_time.ntp_server1 = 192.168.0.5
Web User Interface:
Settings->Time & Date->Primary Server
Phone User Interface:
Menu->Basic->Time & Date->General->SNTP Settings->NTP Server1
local_time.ntp_server2
Description:
Configures the IP address or the domain name of the NTP server 2.
If the NTP server 1 is not configured (configured by the parameter "local_time.ntp_server1")
or cannot be accessed, the IP phone will request the time and date from the NTP server 2.
Example:
local_time.ntp_server2 = 192.168.0.6
Web User Interface:
Settings->Time & Date->Secondary Server
Phone User Interface:
Menu->Basic->Time & Date->General->SNTP Settings->NTP Server2
local_time.interval
Description:
Configures the interval (in seconds) to update time and date from the NTP server.
Example:
local_time.interval = 1000
Web User Interface:
Settings->Time & Date->Update Interval (15~86400s)
Phone User Interface:
None
local_time.time_zone
252
Permitted Values
IP address or domain name
Integer from 15 to 86400
-11 to +14
Default
pool.ntp.org
1000
+8