Against Nadd, maybe a minute or two. I'm not underestimating him in the least, but. . . . here's how I can put it. Other than Obi-Wan vs. Anakin, what prequel duel lasted more than two minutes? And I mean a saber duel, not a Yoda/Sidious-esque fight? None. And of course, even now I think that Ulic could give Yoda a good fight, and even defeat Dooku. But I don't think he could stand up to Nadd or Sadow and come out on top.