notify command is delayed

[Hostmaster]

We do make dynamic updates on our master dns. The notifiying command for the slave is delayed between 3 and 6 minutes, after the master has made the update. Cause we will use it as dynamic dns for dial-up connections, we have to make it send the notifiying nearly immedtiately after the change.
We are using Suse Linux 7.1 and Bind 8.2.3-T9b on  the master server and Suse 7.0 with bind 8.23-T5B on the slave.

Can anybody help me on that ?

thanks
Andreas