We do some upfront diagnosis that can take 1 - 2 days.  Our off-site team events usually run for 3 - 5 days.  Teams that try to skimp on the duration end up wishing they'd taken longer, because they realise what they've missed once they have actually experienced it.

The power of our work is in the depth we reach, and we need a minimum of 3 days to get there, unless we are working with a team for the second time.