We know from fossils the approximate timings of the ancestral splits between coelacanths, lungfish and ourselves. The first split, at about 420 million years ago, is that between the coelacanths and the rest. Then, perhaps 5 million years later, the lungfish split off, leaving the rest of us, now called tetrapods, to make our own evolutionary way. As evolutionary time goes, these splits occurred at pretty nearly the same time, at least compared to the long time over which the groups have been evolving ever since.
