That's common immediately after installing an upgrade. Should be faster the second time. There is no problem to be fixed.
You can always reinstall Snow Leopard. Here's how:
Downgrade Lion/Mountain Lion to Snow Leopard
1. Boot from your Snow Leopard Installer Disc. After the installer
loads select your language and click on the Continue
button. When the menu bar appears select Disk Utility from the
2. After DU loads select your hard drive (this is the entry with the
mfgr.'s ID and size) from the left side list. Note the SMART status
of the drive in DU's status area. If it does not say "Verified" then
the drive is failing or has failed and will need replacing. SMART
info will not be reported on external drives. Otherwise, click on
the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions
from the drop down menu to one. Set the format type to Mac OS
Extended (Journaled.) Click on the Options button, set the
partition scheme to GUID then click on the OK button. Click on
the Partition button and wait until the process has completed.
4. Quit DU and return to the installer. Install Snow Leopard.
This will erase the whole drive so be sure to backup your files if you don't have a backup already. If you have performed a TM backup using Lion be aware that you cannot restore from that backup in Snow Leopard (see below.) I suggest you make a separate backup using Carbon Copy Cloner.
If you have Snow Leopard Time Machine backups, do a full system restore per #14 in Time Machine - Frequently Asked Questions. If you have subsequent backups from Lion, you can restore newer items selectively, via the "Star Wars" display, per #15 there, but be careful; some Snow Leopard apps may not work with the Lion files.
You can purchase Snow Leopard by contacting Customer Service: Contacting Apple for support and service - this includes international calling numbers. The price is $19.99 plus tax. You will receive physical media - DVD - by mail.
After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store.
Same problem for me. There are other threads on the forums about this. It doesn't get quicker the second time either. Some have suggested it's because of iCloud background operations causing slower shutdown. I don't know but it is a bit annoying. The Mac used to be fast to shutdown, now it's like a Windows PC.
Another user has posted a solution to this that has worked for me. Here is the link:
The problem seems to be when you set your AppleID in System Preferences. Removing this (see instructions in the other thread) return shutdown time to just a few seconds.