Such an old question but still appears to be valid even for windows 10 (Seriously Microsoft you should fix it once and for all)
I started window 10 with Windows 10 1703 (15063.1387 - I don't think these minors are important).
I had configured:
After upgrade to Windows 10 1709 (16299.461) everthing stopped working again.
I haved added a registry DWORD key
ActiveWndtrkTimeout with the same value (leaving the old key there) and the raise delay started to work again.
From the MSDN:
0 is the default value.
Note: I want to get one disinformation corrected
There is also a registry entry
HKEY_CURRENT_USER\Control Panel\Mouse. This entry does not change the window raise delay. It changes how fast are the taskbar information & preview shown.
An update 17/12/2020
Here we go again, sigh Microsoft you should really improve your testing!
After Windows 1909 (OS Build 18363.1139) update the hovering delay stopped working again! I have added the deleted
ActiveWndTrkTimeout again, but nothing happened to my surprise. (even after rebooting)
What you have to do Control Panel\All Control Panel Items\Ease of Access Center\Make the mouse easier to use and uncheck the checkbox Activate a window by hovering over it with the mouse click on apply button. Then check the checkbox again and click on apply button again. Now it works again!