Milter-greylist

I just starting using milter-greylist on the email server for my company
and I have to thank the developer and contributors for this software.
It's practically solved our spam problems.  I'm running an FC5 system
and used the rpm from the extra's.  Easy to setup, easy to run, and easy
to customize.

The only problem I seem to have now is dealing with the long delay when
receiving email.  Most of my clients are used to near instant email
delivery.  When I first turned it on, it was greylisting for 30 minutes
and depending on what the sending server retry was, emails were taking
in excess of an hour.

So until I actually run into problems with the program, can I ask for
some opinions on the greylisting time delay and what people have found
to be a good balance of delivery time versus effective spam blocking?  I
just last night reset it to 10m greylisting and that seems to be just as
effective at first glance.  My system services 1 domain with 1 mail
server and roughly 50 clients.