Are you sure you set the time to three minutes and not three hours? Have you checked the reminder on the contact?

Sub AddThreeMinutes()    
    SetReminder 3, True
End Sub
On restarting Outlook you should get a reminder pop up when you next start Outlook (after three minutes). Because of the way Outlook works, you may have to wait a few seconds for the reminder to appear. It does however appear if you have copied the code correctly.