measures are related to tempo, so number of measures cannot be a guide without taking tempo into account. If you have watched the intro to the 'Alive Alive O' book demo this gives an example of fast picture change synced to the 'one, two..' count intro, at around the fastest that is achievable.

Basically the minimum time will be limited by the lcd refresh rate.

If you're still having problems if you like I'll have a look to sort it.