Two counters, a Close count and a Leave Open count; the first count to reach 5 determines the outcome? (A definitive resolution with a maximum of 9 votes.)
A single counter that requires 5 close votes before the queue expires; a Leave Open vote offsets a Close vote, reducing the Close vote count? (If voting was evenly divided, a question could be voted on almost unlimited times without reaching 5.)
A Leave Open vote is just lack of a Close vote; it registers participation in the queue but does not offset Close votes? (Regardless of the number of "Leave Open" votes, a total of 5 close votes results in closure.)
My understanding was that it was #1, but occasional, apparent "odd" things have me wondering.
Sitting in the Close review queue is focussed attention. Three "Leave Open" votes knocks it out of the rounds for a while so that the close vote ageing happens as quietly as running into the question outside of the review queues.