time service event 37

Windows Server 2008 R2

just a few minutes back, the time on our DC changed to 6:05AM while our real time is actually 4PM!

i found this on the event logs:

Log Name:      System
Source:        Microsoft-Windows-Time-Service
Date:          1/12/2014 6:05:02 AM
Event ID:      37
Task Category: None
Level:         Information
Keywords:      
User:          LOCAL SERVICE
Computer:      SERVER1.ACME.COM
Description:
The time provider NtpClient is currently receiving valid time data from time.windows.com (ntp.m|0x0|0.0.0.0:123->65.55.56.206:123).
Event Xml:<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"><System><Provider Name="Microsoft-Windows-Time-Service" Guid="{06EDCFEB-0FD0-4E53-ACCA-A6F8BBF81BCB}" /><EventID>37</EventID><Version>0</Version><Level>4</Level><Task>0</Task><Opcode>0</Opcode><Keywords>0x8000000000000000</Keywords><TimeCreated SystemTime="2014-01-12T03:05:02.093750000Z" /><EventRecordID>85303</EventRecordID><Correlation /><Execution ProcessID="904" ThreadID="2572" /><Channel>System</Channel><Computer>SERVER1.ACME.COM</Computer><Security UserID="S-1-5-19" /></System><EventData Name="TMP_EVENT_TIME_SOURCE_REACHABLE"><Data Name="TimeSource">time.windows.com (ntp.m|0x0|0.0.0.0:123-&gt;65.55.56.206:123)</Data></EventData></Event>

for now, i have managed to correct it manually but why this happened? Should I change NTP servers?

Appreciate any help.