Our databases are growing very fast. And after deleting lots of emails, of course, Exchange doesn't free up the white space. To do so we have to either create a new database and migrate users to it, then delete the old d/b OR use the offline defrag utility... eseutil.exe /D path\to\file.edb.
My first choice would be the create a new database and migrate. That way the org mail is not down. But if we were to decide to go the offline defrag route, how can we get a general idea of how long it would take? We have five database each approximately 100Gbs on high availability virtual HDDs on ESX VMs with 12GBs RAM. I'd hate to tell my boss it could take 6-12 hours and it take 3 days...LOL.