[VadeRetro]

There probably haven't been any new families of animals evolving in thousands and thousands of years.

Quite likely. Then throw in that the Linnaean system was created in 1757 based upon the way things looked 245 years ago. Then consider that divergence isn't sudden. Throw in that higher taxons are arbitrary, based upon the retrospectively considered importance of evolved traits.

[Hunble]

Obviously, it would depend upon the birth rate.

For slow birth rates with the larger animals, I would expect a new family to emerge in about 100,000 years.

Actually, it should be a function of the number of generations, and not specifically time.