Jacko
You're not too far off the mark but it would be pointless to define too closely how many hours one needs to display a big piston - or anything else for that matter. Some catch on quickly and others take longer. Some are naturals and others more mechanical. It is much more important that the individual stays well within his and the aircrafts' limitations and that he has the right temperament for a display pilot.
Unfortunately, we have lost far too many old and irreplaceable aircraft on the display circuit and it does seem that some pilots think they can fly them without much training simply because they are slower than their regular steeds. However, all aircraft bite fools and the old aircraft bite more often and more easily.
Reichman
If the BBMF display is 10 minutes too long for you, take a break next time they display whilst everybody else enjoys them.