I can't find a definitive answer to the man-hours, but I would say that a lot less time was spent producing the animation for 101 Dalmatians (1961) when compared with the previous movie, Sleeping Beauty (1959).
Up until the end of the 1950s, artists would draw the the scenes and characters on paper, and then they would be traced by inkers onto animation cells before colouring and then photography. As you can imagine, inking could take quite some time - especially in complicated scenes.
By about 1959, Ub Iwerks (who had co-created Mickey Mouse, along with other Disney creations) had developed a Xerox camera that could print the animators' artwork directly onto the cels, removing the need for hand inking. However, the process produced a scratchy line effect, rather than replicating the more lavish ink lines from the manual process. This was first used in Sleeping Beauty for the thorny forest scene, where the scratchy lines probably enhanced the feeling of the scene.
101 Dalmatians almost didn't happen, as Sleeping Beauty cost $6 million and only made $5.3 million gross on its first theatrical run, and Disney almost closed the animation department following this. As you can imagine, inking scenes with 101 dalmatians would have been incredibly complex, laborious, and expensive.
So, Iwerks' xerographic process was brought in - and the film was produced for only $3.6 million with an extra 4 minutes runtime over Sleeping Beauty. There were probably other cost-cutting measures, but Chuck Jones estimates that the xerographic process was the biggest contributor to the saving.
The Advent of Xerography: Disney’s One Hundred and One Dalmatians