avast is a resident on access scanner, it checks files that are created or modified or when accessed. It doesn't do a daily scan (on-demand), you can however, do this if you have the Pro version or there is a work arround for the home version.
HOWTO: Scheduled Automatic Scans w/ Free Version!, this is obviously not as flexable as either the manual on-demand scan or the Pro version. It will however scan every file, something that will take extra time.
I scan my system (all HDDs) manually as a part of my weekly maintenance tasks.
Auto updates - iAVS as required but usually twice a week and it checks every time you connect to the internet. - Program updates are now checked once a week (to avoid server overload) and if one is available it will let you know.