That seems like a pretty long time unless you have a very large drive or drives with many compressed files or are scanning a large external USB drive. See if this post helps - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2008959&SiteID=2
Another reason for slow scan performance is a conflict with other a/v software installed.
If not, contact support -
How to reach support - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
If it fails to validate your subscription, select the option that you are using a trial or beta copy and you can proceed to email support without validation once you've signed in.
-steve