Extend or Increase "Exchange 2007 or 2010" OWA Automatic Log off time

When you trying log in to OWA you can select "This is a public or share computer" or "This is a private computer" options.

• Public: is the default option. If you use this option your username will no saved and your session will terminate after 15 minutes.
• Private: is intended for private computers. If you use this option your username to be remember automatically, however you need to retype your password each time, and your session will terminate after 8 hours.

For you modify  this values you need create one or both of above key. For this task following the below steps:

1. Click Start, in "Search programs and files" type "regedit" to open the Registry Editor.
2. Locate the following registry subkey: HKEY_LOCAL_MACHINE/System/CurrentControlSet/Services/MSExchange OWA.
3. In the right panel, right click New and select DWORD value if your system is 32 bit or select QWORD value if your system is 64 bit.
4. Rename "New Value #1" for PublicTimeout.
5. Right click in PublicTimeout REG-DWORD created and select Modify...
6. In the Value data type 30, and in Base panel click to select Decimal.
7. Click Ok.

* For create PrivateTimeout key follows the same steps used above. After That close the  Registry Editor.

Finally restart IIS Admin Service to take effect the change. Now OWA Timeout in Exchange is restricted and working