Try this (from their Help file);
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Edit scheduled scans
You can change the schedule of any scheduled scan, including the weekly full system scan.
To edit a scheduled scan
Start Norton AntiVirus.
In the Norton AntiVirus main window, click Scan for Viruses.
In the Scan for Viruses pane, In the Scan for Viruses pane, select the scan that you want to schedule.
If you click the button next to the scan name, the scan runs.
Under Schedule Task, click Schedule.
Change the schedule as desired.
Click OK.
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Hope it works,
Cd