When you place your mouse cursor over the taskbar button of a running application, a small thumbnail of the application will appear. By placing your cursor over this thumbnail, you will see a live preview of the running application and all other applications that are running will become transparent. You can change the delay time for these live previews to better meet your liking by following these steps.
1. Click the Orb (Start Button).
2. Go to the Search programs and files textbox and input regedit.
3. Select regedit.exe from the results.
4. When the UAC prompt appears, click the Yes button.
5. In the left pane of the Registry Editor, go to (and select):

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
6. Right-click in the right-pane.
7. Click New and select the appropriate DWORD for your system.
8. Name the new DWORD ThumbnailLivePreviewHoverTime.
9. Double-click the new DWORD.
10. In the Value data textbox, input the desired number of milliseconds that you want to set the delay time to.
11. Select the Decimal radio button.
12. Click the OK button.
13. Restart your computer for the change to take affect.
