I find claims that you'll cut time on small projects by writing tests to be unsupportable. Larger projects may show gains as the complexity of a job mounts, but I don't have any hard data to show you.

As a counter point I find that doing test-first testing does cut the time - even for smaller projects. The time I spend writing tests is more than made up by the time I save by not debugging broken code.

Of course I too have no hard and fast numbers - just personal experience :-)