sub domain options

[chris at rockfort.com]

I am having terrible time trying to get 2 sub domains to perform properly.
at around 4 am til 10am the records disapears. In other words if you try to
get the resource http://sub.mydomain.com there is no DNS record, yet the
main record http://mydomain.com is always avail able and works properly in
both cases. In each zone file the sub domain is refernced as an "A" record
like this
sub  IN A 1.2.3.4

I would to create a new zone file for these sub domains, but I am not sure
if that would be "illegal". In other words

$TTL  86400
$ORIGIN sub.domain.com

and then configure the named.conf to refelct this new zone.. Please keep in
mind that this sever is the authorothy for http://mydomain.com and that
this zone is also on the same server that I intended to do this with...

I just feel that this woould solve my problems with these sub domains
disapearing....

Chris