This setting is used to enable the local machine to act as a Network Time Protocol (NTP) server. When enabled other machines can synchronise their clocks with this machine.
Open your registry and find or create the key below.

Create a new DWORD value, or modify the existing value, called "LocalNTP" and set it according to the value data below.

Exit your registry; you may need to restart or log out of Windows for the change to take effect.

Registry Settings
System Key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters]
Value Name: LocalNTP
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disabled, 1 = enabled)