[Callers] Card boxes and Dance ending

Hello, So most callers have dance cards, and all dances have to be ended at some point. I have my ways of doing it, of course, and I've asked a lot of callers about theirs, but haven't found anything I'm quite happy with. Basically, how do you organize your box of dance cards and why do you like it that way? And, How do you figure out when to end a dance? Of course finish with all couples in, but how do you decide when it's about time to end it? Some callers simply set a timer, or count a number of times through, or end when couples have come back to where they started. What do you do? Does anyone try to gauge the energy of the dancers on the floor and end when it seems right? Thank you very much, David Giusti