"Tiempo" means time, as in the passage of time, but "veces" refers more to a timed occurrence, for example: "No tengo tiempo para estudiar" - I don't have time to study. "Cuantas veces te lo tengo que decir?" - How many times do I have to say it to you? As you can see, it doesn't really mean the same, and I can't think of an example where you would substitute one for another with the exact same meaning.