Have you made any changes to the pre-defined Full scan default settings ?
Have you done a Full scan before and was that similar in duration ?
Personally I feel a Quick scan is more than adequate as it covers the more critical files/areas, the Full scan goes to the next level of risk.
- With a resident on-access antivirus like avast, the need for frequent on-demand scans is much depreciated. For the most part the on-demand scan is going to be scanning files that would be otherwise be dormant or inert. If they were active files then the on-access file system shield would be scanning them before being created, modified, opened or executed.
I have avast set to do a scheduled weekly Quick scan, set at a time and day that I know the computer will be on. If for some reason my system wasn't on, no big deal I will catch up on the next scheduled scan.
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I see from your signature that you have SAS and MBAM are either of these resident on-access ?
If SAS Pro has resident scanning enabled try it disabled when avast is scanning.