In that case as you have NTP inplace and working, I personally reckon you should be able to ignore these events of Linux attempting to grab time source info from the "hardware".
Like I say, it's a time related error event. The the effect of having an unstable time source is that your logs and time-dependant policies may not work as expected. As long as the SWG has the right time (from NTP in your case) then I wouldn't worry too much about it.
If it is a major concern, then I'd suggest logging a case with Symantec on it.