You don't have a "." at the end of "_kerberos._udp.GROUP-42.SNOOPY.ISP", so named is appending the zone origin to the end of that string because it is not a Fully Qualified Domain Name (FQDN).
Consequently you don't have a record for "_kerberos._udp.GROUP-42.SNOOPY.ISP" you have a record for "_kerberos._udp.GROUP-42.SNOOPY.ISP.$ORIGIN" ($ORIGIN will be either the name of the containing zone (the default) or whatever you have set it to if you have defined a different origin in the zone master file.)
Try putting a "." at the end of the record label, increment the zone serial number in the SOA, and reload the zone.
EDIT: You may also have another problem, as the lack of a record in your zone should not result in a timeout doing a query for that record. But fix the missing "." first, and then if you are still having problems post the entire output from the failing dig command. The result is important, as is the server section. It wouldn't hurt to use the "dig @server" syntax to specify the server you are asking, or dig +trace, either..