Is there any way to estimate an expire/reduce

Hello

We are getting ready to do a one year expire/reduce on our very large and old post offices. Is there any way to estimate how log it would take, or to run it in a
'test mode' that will show how long it would take without cleaning up the mail.

Also when it is ran on the post office, does it lock the entire post office, or just the accounts it is working on at that moment.

Any thoughts will be appeciated.

Chris T.