Trust Relationship Replication Issues

Hi,
I have 2 Windows 2000 domains [Not in the same forest] that have a 2 way trust. When a user in Domain1 is added to a group that should give him access to Domain2 it takes about 12 hours for the change to be made on Domain2. Can I manually forcethe change to be made instantly. Alternatively, where can I set a replication schedule up?

Cheers,
Damian