Schedule STILL isn't going on the time I set

I just noticed when you get the results of your scans, I clicked on the "gear" icon & it HAD my scan scheduled at 6:30 pm & it's a deep computer scan.  We have a LOT of stuff on our computer, including AOL & Facebook & our business stuff.  At 8:45 pm when I come back here it's only like 23% complete.  Is that normal?  Do you think it's actually starting at 6:30 & because I checked "deep computer scan" it's taking a LOT longer?  This scan could actually take a few hours, can't it?  ugh…