Because the scheduled scan can slow down your computer's performance, you should run the scheduled scan at a time when it will least affect your work. In other words, schedule the scan for a time when the computer is on but you aren't using it. By default, the time set is for around 2 A.M., but if you work at night, consider changing the time to sometime during the day.
To make sure the scan runs when your computer isn't being used
Click Settings, and then click Scheduled scan.
If the Start the scheduled scan only when my computer is on but not in use check box is not selected, select it now, and then click Save changes. If you're prompted for an administrator password or confirmation, type the password or confirm the action.