When you write a new key, or Value Name, or change / delete a Value Name, Windows records the data time in the registry key.
To view the Last Write Time for a key and sub-keys, use REGEDIT.EXE to select the key, right-click it, and press Export. Toggle the Save as type box to Test Files (.txt). Navigate to a folder and type the file name into File name. Press the Save button.
When you open the file in NOTEPAD.EXE, each key in the file has a Last Write Time attribute.
Class Name: <no class>
Last Write Time: 01/28/2006 - 04:06