Sure, but you realize that even a cursory consideration questions whether that's a meaningful number in and of itself?
Species A was on the planet for one million years. Species B was on the planet for 500,000. So what? What are you supposed to get from this? That A was somehow better at life than B? Okay, fine. Let's say that.
But, what if we look and see that Species A lived in a time of little change in the environment or the other life around it. And Species B lived in a time of great upheaval and change. Does it mean something different now? Now... maybe B was more impressive, for having done the feat it did, considering the time? Okay, fine, that makes sense. Let's say that!
Oh, wait. But we find that while Species B was living in a time of climate upheaval and change... none of the other species around it found much need to change, either. Everyone got through that half-million years okay. So, maybe Species B really isn't all that impressive after all?
Raw and simple data outside of its context doesn't usually reveal a whole heck of a lot about the natural world. If we want to make a declaration, and we find a simple measure right at hand... that's kind of a sign that maybe we are assuming our conclusion from the start, rather than having our mind open to figure out first what our question really ought to be...