We have 2 kinds of Check outs, Short term and long term. If you click the drop-down of a document in a Doc lib and choose “check out”, that is a long term. When Word opens the document in “Read-Write” mode, it places a short term checkout on the document. In Office 2003 the short term checkouts were 10 minutes; in 2007 it is changed to 60 minutes. The short term check-out refreshed automatically as long as Word is open. There is no way to force the expiration of a short term checkout.
The discard check-out option available in the drop-down menu of a document library is used only for the long term checkout. If a user opens a document from a document library in the Read-Write mode, then that creates a short-term lockout and no other user can edit the document till the first user closes it. You can find the expiration time in the 'CheckoutExpires' column of the AllDocs table. It becomes NULL only when the first user close the document.
The interesting part of this behaviour is this. If a user does a short check-out and keeps the client application ‘Word’, open with the document and goes away for the weekend, then no other user can modify this document till that user returns and closes ‘Word’. Not even the administrator has the control to get this document back to read-write mode.
Windows XP with Office 2003 / Office 2007:
Default short term checkout Expire time is 10 minutes.
If the opened document is closed, the lock will be released immediately.
If the application (Winword.exe) crashed then we have to wait for 10 minutes and the lock will expire in 10 minutes
Windows VISTA with Office 2007:
Default short term checkout Expire time is 60 minutes.
If the open document is closed, the lock will be released immediately.
If the application (Winword.exe) crashed then the lock will be released immediately.
As per KB http://support.microsoft.com/kb/899709/en-us the suggested workaround is "wait 10 minutes before you click Edit in ProgramName to open the document again."