In short: when in outlook (after you did setup your account correctly) use the following shortcut: To open the Send/Receive Groups dialog box, press CTRL+ALT+S.
There you can adjust the time (default 30 minutes). We advise not to put this lower as 5 minutes; preferable 10 minutes to avoid to many POP checks from your account towards the server.
The long explaination from microsoft you can find in the official microsoft KB article here: http://office.microsoft.com/en-us/outlook-help/change-how-often-a-pop3-account-sends-mail-and-checks-for-new-items-HA010356435.aspx
