seondary zone replication

[Tester]

Hi there,
I replicate 2 zones between a W2K3 server and Unix Bind 9 server, each
zone is primary zone on each of the boxes above. W2K3 has an AD
integrated zone that gets replicated to Unix and Unix has a Bind 9
zone that gets replicated to windows. How can I make sure replication
happens only once a day? I noticed sometimes it is replicating quite
frequently during the day and I am concerned this might affect the
windows machine.
Thank you very much, T