As a dancer, I have found a lot of callers aim for 4 per hour, and this feels way too long for several reasons:
- Especially in warm weather, dancers get tired
- Musicians get tired, too.
- People involuntarily sitting out have to suffer through a longer out time.
With dances more like the 8-9 minute range, I've find dancers are more likely to dance more, less likely to leave at the break, and are generally giving better energy to the band

That said, I'd caution against any method that places consistency above feeling out the audience. Factors that might affect dance length:
- temperature
- timing to end of a break / evening considering any unexpected changes (long walkthrough, slow hands 4, etc)
- dance difficulty was mis-gauged, thus a desire to move to a new dance rather than watch dancers struggle too long
- band and dancers are in a groove that you may just want to hang onto a bit more (when my dancers are starting to hoot, perhaps it's not the best time to signal 3 more...)

Ron Blechner