The short answer is NO, but it will be scanning activity very shortly after boot. Avast by comparison is comparatively light.
If you have a lot of programs allowed to start on boot, then this activity will be scanned, but even that wouldn't take 30 minutes.
Previously there used to be an anti-rootkit scan after 8 minutes, but again that shouldn't take long at all.
Also Avast would be doing a check for Virus definitions and program update availability, but again that shouldn't take long at all. Seconds to check if updates are available.
Have you manually set up any Avast Scans ?
What Avast version do you have installed ?
What other security based software do or did you have installed ?
