The number of seconds to wait before restoring completion windows.
Once the completion window has been displayed, if the user then goes
on to type something else, that completion window will be removed from
the display (actually, the original window configuration before it was
displayed will be restored), after this many seconds of idle time. If
set to nil, completion windows will be left on second until the user
removes them manually. If set to 0, they will disappear immediately
after the user enters a key other than TAB.