FYI - the smaller ISP in my area thinks 7AM is a good time to re-load EIGRP, IS-IS, OSPF, BGP updates. When this happens, all traffic on the pipes affected by the particular backbone go dead for about 5 minutes. This affects only certain backbones at a time, not all.
This would seem more likely to be the issue (or the reboot/reload of an edge/border router), then your DNS non-issue.
