Note that you’ll have to use the Local Drives option to get that to update properly. Working via Folders, even if you select the whole drive, for some reason doesn’t do it.
Maybe this was an “unheralded” fix in one of the more recent versions, but it used to be that only Local Drives would update the status screen properly. I think there was one or more threads about this quite a while back.
I know that it was meant to be changed so that folder selection scans would be included. I did a folder selection scan this afternoon when testing the UPX unpacking scan using on-demand scan I selected the folder with the UPX file in it and scanned that it hasn’t been recorded. The date of last scan still shows 17/09/2006 00:19 which was a full local disks scan.
No, the meaning hasn’t changed - this date is “the date of the last successfully finished scan of all the local disks”. But I believe it should work from Folder selection as well (provided you select all the local disks, and possibly more, of course).
The time taken by avast’s on-demand depends on several factors, mainly the Sensitivity, Quick, Standard or Thorough, add to that if you select scan archives. Your system CPU and RAM also play a part.
The thorough is also by its design very thorough and perhaps a little overkill for routine use, were a Standard scan without archives should be adequate.
I have only ever done a through scan with archives once shortly after installation just to ensure a clean start state, but with XP for example avast will do a boot-time scan after installation if you select it, this I believe will be quicker and reasonably effective. Like everything in life things are a compromise.