One little know quirk in the Time Server system, is that say you had more than one Computer addressing the vTime Server, and they happened to request Time within 4 seconds of each other, it could be tagged as a Denial of Service Attack, and hence be negated for a while.
I must ask a question at this point... Why must you use Apple's Time Servers if other Time Servers work?
For instance, I just turned OFF automatic update, set my Month, Year, Day, and Time off by one on each, used "time.nist.gov", set automatic update back ON, and within about 30 seconds everthing was back to correct!?