Purge all mail items older than 45 days on the 15th of the month.

We recently upgraded from Exchange Server 2003 to Server 2010. In 2003 on the 15th of every month I would run the mailbox management process and have delete all items older than 45 days. It was great that you could create a query and have only those users who met the criteria purged. It appears with 2010 that the process is running constantly. If I set up a 45 day retention policy then every day it would delete everything older than 45 days. That is not what I want. I want to be able to press a button or something and have it run the purge. Is there any way to do that under 2010? 

Thanks