Override Norton scheduled scans with customized scans

In Norton Internet Security I try to schedule my own scans - during off-hours - and stop the regular Norton full scans.  However - Norton ignores my setting and continues to run right in the middle of the day when I try to work.  How can I disable the Norton scans?  How can I activate my customized scan schedule?  And what can I disable within Norton to conserve CPU - Norton as is configured now is bringing my CPU to its knees - yet have effective coverage?