Windows – Why is the shutdown time so long

Windows services takes the most of shutdown time. Some services, like those that have network-related shutdown operations or have to save large amounts of data to disk, might require more time and so Windows Vista allows a service to request pre-shutdown notification. When Windows Vista shuts down, the Service Control Manager first notifies those services asking for pre-shutdown notification. It will wait indefinitely for these services to exit, but if they have a bug and don't respond to queries, the Service Control Manager gives up and moves on after three minutes.

You may check your event viewer for any errors. see if any particular application is causing the slow shutdown.

Here are a few registry tweaks to speed matters up:

Auto End Task

This registry setting ends the running task and automatically shutdown the application

Go to Start > Run, type regedit to open Registry Editor.

Navigate to HKEY_CURRENT_USER\Control Panel\Desktop

Scroll down to find the registry key called AutoEndTasks. Right-click on the key, select Modify and change the value to 1.

Exit Windows Registry after making changes.

Wait To Kill Application

This registry key function is to set the time interval for Windows before killing the applications to shutdown the computer.

Navigate to: HKEY_CURRENT_USER\Control Panel\Desktop

Scroll down to look for the Registry Key called WaitToKillAppTimeout, right-click on it, select Modify and Change the value to 1000.

Hang Application Time

This registry key sets the hang time of the application before closing.

Navigate to: HKEY_CURRENT_USER\Control Panel\Desktop

Scroll down to look for the Registry Key named HangAppTimeout.

Right-click on it, select Modify and Change the value to 1000, exit Windows Registry

Clear Page File Before Shutdown

Last but not least, make sure Windows doesn't clear the pagefile on shutdown:

Navigate to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management

Scroll down for the Registry Key named ClearPageFileOnShutdown, if this is set to 1, right click on it, select Modify and Change the value to 0.

Wait To Kill Service Timeout

This registry key sets the time for Windows to wait before ending services related to Microsoft.

Navigate to: HKEY_CURRENT_USER\Control Panel\Desktop

Look for the Registry Key named as WaitToKillServiceTimeout, right click on it, select Modify and Change the value to 1000.

Source

p.s.: if you're looking for the easy way out, grab Superfast Shutdown, it does what it says on the tin, guaranteed :)