snooker,
Unfortuantely, Avast cannot be set to a schedule.
Nor can it be set to "complete" a scan before taking action on an infected file.
The reason it stops at an infected file is to limit the exposure of your computer to a potential hazard.
Assuming that no virus is found, Avast will "report" the results to you in the event that some files could not be accessed for the scan. These are usually password protected system files, or those files protected by the System Restore.
As for a "time" feature.....not a bad idea.
Send the suggestion to Avast at their contact address or directly to support at support@asw.cz
Thanks.
Techie