Here's the full text of the error received:
the operation failed because:
Failed to configure the service NETLOGON as requested.
"The wait operation timed out"
and in the dcpromo.log is the following:
07/07 09:02:24 [INFO] Informed NETLOGON to deregister records
07/07 09:02:24 [INFO] Stopping service NETLOGON
07/07 09:04:24 [INFO] StopService on NETLOGON failed with 258
Change the first DNS setting on your network card to point to your new
DNS server, not the server you are currently demoting. Once you change
the DNS setting to the new DNS server you will be able to demote the
server without this issue.