The minimum level you can set through the GUI is 15 minutes.
This is how you can change this through a registry setting: ScheduleAccelerator.
Remember, this connector is only available for a Small Business Server !

1. Locate and then click the following registry subkey:
“HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/SmallBusinessServer/Network/POP3 Connector”

2. On the “Edit” menu, point to “New”, and then click “DWORD Value”.

3. Type “ScheduleAccelerator” (without the quotation marks) as the entry name, and then press ENTER.

5. On the “Edit” menu, click “Modify”.

6. In the “Value data” box, type the value that you want, and then click “OK”. To determine the polling interval, the value that is configured on the “Scheduling” tab in the GUI is divided by the value that you type for the ScheduleAccelerator entry.

For example, if a 15 minute interval is specified in the GUI and you set the value of the ScheduleAccelerator entry to 3, the connector will poll ever five minutes.

7. Quit Registry Editor and reboot the server.