<p>I believe the "shiur" of yichud - the minimum amount of time of yichud to be a violation - is not the amount of time people spend in yichud.&nbsp; Rather, it is the amount of time of expected privacy (minimum opinion is about 35 seconds).&nbsp; So, for example, a man is not allowed to lock himself alone with someone else's wife for 10 seconds (I think&nbsp;Tosafos would also assur that, right?).&nbsp; The question is (like in an elevator), in this situation, is he reasonably certain his&nbsp;privacy won't be disrupted for 35 seconds.&nbsp; So even if the elevator door stays closed for 10 min, or nobody walks into the store for 25 min, those are not yichud because someone COULD come in.</p>