[CentOS] ntpdate odd behavior

I noticed this morning that my ntp time was not correct on machines.

So I manually ran "ntpdate time.apple.com" on my clients, I got
7 May 08:46:43 ntpdate[10550]: no server suitable for synchronization found

then I ran "ntpdate -d time.apple.com" and it worked .
filter offset: -163.446 -163.446 -163.446 -163.447
         0.000000 0.000000 0.000000 0.000000
delay 0.20570, dispersion 0.00049
offset -163.447341
 7 May 08:46:25 ntpdate[10519]: step time server 17.253.2.243 offset
-163.447144 sec

then I ran "ntpdate time.apple.com" again and got the above error again.

Any idea what that is about? Why is ntpdate giving the error?

This is on centos 6.6 x86_64 and same result on 3 machines.

Thanks,

jerry