If you are referring to the scheduled scans under Real Time scanning, go to the Scheduled Scan Settings and see if the first box titled Scan Using Minimal Resources is checked. If so, you may want to uncheck this and try another scheduled scan.
My scheduled scans were taking about 5 hours and this fixed it for me and put it back in the 1 hour range. This may have a performance impact if you are using your system while the scan runs. With mine, it was noticeable but still very useable.