Intrasite (same site)= 15 seconds Windows 2003 and 5 minutes Windows 2000 http://technet.microsoft.com/en-us/library/cc728010(WS.10).aspx
180 minutes is correct for the default intersite schedule - http://technet.microsoft.com/en-us/library/cc759160(WS.10).aspx
15 minutes is the lowest amount you can set using the GUI. If you want intersite replication to be faster than that you would enable somthing called change notification.
Thanks
Mike
