If you install AVG and use all the default settings, you will find that the AVG wants to scan your computer every day at either 8:00am or 12:00pm (noon). Because the complete system scan can take up to an hour or more to complete (depending on the number of files on your computer), it can be extremely inconvenient to have the scan slow your computer down when you are trying to work on it.
You can stop the scan if you need full power from your computer by RIGHT clicking the AVG scan icon by your clock, then click Stop All Scans or you can change the schedule to a more convenient time. Here’s how to change the schedule of the AVG daily scan:
And yes, your computer has to be on for the scan to run. If you choose a time in the middle of the night, but don’t normally have the computer on at night, simply leave the computer on over night once a week. The day doesn’t matter.