I use AutoHotKey to perform this function.
AutoHotKeyAutoHotKey is a Windows scripting application and language.
Check out the site here: http://www.autohotkey.com/
The code I use is below, it would be easily modifiable to insert the time and change the slashes to hyphens if that is what you prefer.
+!d:: ;Shift-Alt-D: Insert current date
SendInput %A_DD%/%A_MM%/%A_YYYY%
return