ESXi and Domain Controller HP BladeCenter time with NTP and time drift

I had a customer that just virtualized there last domain controller, this was the PDC, and this was configurered to use NTP: dk.pool.ntp.org, the same was the case for the ESXi hosts. But for some reason the time was drifting about 3-6 minutes every day. After some investigation where we could see that syncing the domain  controller manuelly fixed the problem for a shot while, and looking at the ESXi hosts: "ntpq -np" it was obvious that it took a long time to do the time sync from external sourse.

After some more invistigation, we discovered that the HP BladeCenter was synchronizing time from this domain controller, and changing it to: dk.pool.ntp.org fixed the problem.