The time wail be totally dependant on your system, performance, qualifying files that will be covered by the VRDB (not all files are, usually system files, exe, dll, etc.). The first scan is likely to take longer than subsequent scans, I do mine every two weeks as a part of my system maintenance and it takes 7 minutes.
I believe the location of the VRDB is "C:\Program Files\Alwil Software\Avast4\DATA\integ", but there is nothing that you can do with the VRDB avast.int file.
