One way would be to unschedule your scans before shutting down your PC for an extended amount of time.
Your system is bogging down because there are too many processes running at once (system resources).
Since Avast has real-time on access protection, imo
daily scheduled scans are not needed and a waste of system resources. Real-time protection is not resource intensive and, with a top-line a/v, has 99% or more efficacy. Your system will run faster and quicker if you do not run scheduled scans.
The only viruses or malware you may find with a manual scan will be in archived files, and that will be almost all the time. Archived files cannot harm you until they are opened, and then real-time protection will step in.
https://en.wikipedia.org/wiki/Antivirus_software#Real-time_protectionPoint is to prevent infection in the first place. Real-time protection does that. If you are looking to prevent infection by routinely scanning on a daily basis, after the fact, the horse already left the barn a long time ago.