not sure it's working

I know a deep scan can take a long while (program says over an hour). When I start a scan on my drive, it quickly shows 0% with 282 files found. However, where it says calculating time for scan, it never shows anything. So far, I have let it sit at 0% with 282 files for nearly an hour, but it doesn't seem to be doing anything else. How long can I expect it to take on a 1TB external drive (that was about half full)? Also, how can I be sure it is working after this point?

Thanks,

Think 5-10 hours or more