When Does The IE Zone DNS Update?

The IE zone (IEDR) reload (refresh) the IE zonefile four every odd hour, ie.01:00,03:00,05:00,07:00,09:00,11:00,13:00,15:00,17:00,19:00,21:00,23:00 hrs. Any DNS changes to an IE domain where the nameservers are being changed will only happen after a full reload or refresh