If you also selected scan archives, yes it could be a long duration, though 22 hours and not complete is certainly strange. How much data is actually on these 200GB HDDs ?
What other security based software do you have that might have an impact, like anti-spyware, etc. ?
Do you have anything else running in the background ?
Archive (zip, rar, etc.) files are by their nature are inert, you need to extract the files and then you have to run them to be a threat. Long before that happens avast's Standard Shield should have scanned them and before an executable is run that is scanned. 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.
