Regrettably, as the many threads relating to 'Last Week's Ref' make clear, there are many of our colleagues who opt for an easy life and so don't enforce the 'Rules' as appropriately as they should. Therefore players may come into games under the misapprehension that they can 'get away with stuff'' and therefore some referees choose to nip this notion in the bud pre-game. And of course, you're right, no referee is ever going to say something like '14 seconds is fine' . However, if a referee was particularly stringent and hard core on 'six seconds and no longer' then he might choose to pre warn the two keepers to avoid a surprise the first time he penalises this! Make sense?