if your Windows update for Windows 7 is taking to scan, even after many hours… it’s possible that your Windows 7 is in need of a patch to for it’s “patching service”.
Since Windows Update by this time (end of October 2016) is not able to get to the update server to get the update on it’s own, it will need a bit of help from you, the user/administrator. The patch was first released with KB 3161647, then superseded by KB 3172605, and then superseded again. I used the patch for KB 3172605 to resolve the problem I was seeing.
Hope this is useful for you.