In order to change the NTP to point to a different source, you will need to modify the registry for the PDC emulator server. Usually this is the first domain controller in your network assuming you didn’t change the FSMO roles for it.

Registry Change Location:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters

1. Change the ‘Type‘ key to ‘NTP‘
2. Add the ‘NtpServer‘ key (This is a string value) and add the new source address to this. This can be an IP address too.
3. Close the Registry window and restart the ‘Windows Time Service‘ under Services
4. Wait and see if computers in your domain gets the time update or not. Usually depending on your setup, it will take 45minutes or less. If not, you can initial the sync by typing ‘w32tm /resync /rediscover‘

Information: Time Stratum order
1 External NTP time source
2 PDC emulator of the forest root domain
3 Domain controllers in the forest root domain or PDC emulators in child domains
4 Workstations and member servers in the forest root domain or domain controllers in child domains
5 Workstations and member servers in child domains

W32Time service registry values
*** From the Microsoft site ***

* AvoidTimeSyncOnWan : REG_DWORD (optional)
Prevents the computer from synchronizing with a computer that is in another site.
0 = the site of the time source is ignored [default]
1 = the computer does not synchronize with a time source that is in a different site
* GetDcBackoffMaxTimes : REG_DWORD (optional)
The maximum number of times to double the backoff interval when successive attempts to find a domain controller do not succeed. An event is logged every time a wait of the maximum length occurs.
0 = the wait between successive attempts is always the minimum and no event is logged
7 = [default]
* GetDcBackoffMinutes : REG_DWORD (optional)
The initial number of minutes to wait before looking for a domain controller if the last attempt did not succeed.
15 = [default]
* LocalNTP : REG_DWORD
Used to start the SNTP server.
0 = do not start the SNTP server unless this computer is a domain controller[default]
1 = always start the SNTP server
* NtpServer : REG_SZ (optional)
NtpServer : REG_SZ (optional) Used to manually configure the time source. Set this to the DNS name or IP address of the NTP server to synchronize from. You can modify this from the command line by using the net time command. Value is blank by default

Note If you enter multiple NTP entries you must separate the entries with a space. For example, if you enter two different IP addresses for two distinct NTP servers, you must separate the entries with a space. Do not use a comma to separate multiple IP addresses or multiple fully qualified domain names (FQDNs).
* Period : REG_DWORD or REG_SZ
Used to control how often the time service synchronizes. If a string value is specified, it must be one of special ones listed below. If you specify the string value by using the numbers (65535 for example), then create the value as a REG_DWORD. If you use the word to specify the string value (BiDaily for example), then the entry should be created as a REG_SZ.
0 = once a day
65535, “BiDaily” = once every 2 days
65534, “Tridaily” = once every 3 days
65533, “Weekly” = once every week (7 days)
65532, “SpecialSkew” = once every 45 minutes until 3 good synchronizations occur, then once every 8 hours (3 per day) [default]
65531, “DailySpecialSkew” = once every 45 minutes until 1 good synchronization occurs, then once every day
freq = freq times per day
* ReliableTimeSource : REG_DWORD (optional)
Used to indicate that this computer has reliable time.
0 = do not mark this computer as having reliable time [default]
1 = mark this computer as having reliable time (this is only useful on a domain controller)
* Type : REG_SZ
Used to control how a computer synchronizes.
Nt5DS = synchronize to domain hierarchy [default]
NTP = synchronize to manually configured source
NoSync = do not synchronize time

The Nt5DS setting may not use a manual configured source.

Note When you join a Microsoft Windows Server 2003-based computer to a domain, the computer may not synchronize its time setting with the time setting of the domain controller if the Automatically synchronize with an Internet time server check box in the Date and Time Properties dialog box is not selected. The default option (NTP) for Windows Server 2003 workgroup computers is disabled if the Automatically synchronize with an Internet time server check box is not selected. When you join the computer to a domain that has this setting, the default synchronization type (Nt5DS) for computers that are joined to a domain is not set and the time service does not synchronize from the domain hierarchy.