Most of them are pretty short. Goku vs Cell is a good example. Goku and Cell weren't fighting for a significant amount of time before Goku's stamina was low enough to considering taking a senzu. Majin Vegeta and Goku were equals, and they dealt massive damage out before Gohan and Dabura could even begin to fight again.
But it seems like the stronger the power/transformation, the faster the fight will end.