I only start writing tests once my startups profitable and stable (if that ever happens). TDD is just not as important as getting a product out the door.
There's not always a "do TDD, develop slowly" vs "do no TDD, develop quickly" dichotomy.
If you're doing it right, TDD should speed you up. It adds some guaranteed extra time to your plans up front but significantly reduces all of the hidden costs of wasting hours debugging bugs that unit tests would have picked up.
So I might know developing a particular app might take 10 hours without tests, 15 hours with tests, but if I waste more than 5 hours fixing a myriad of bugs, the TDD approach still wins. (The constant reward cycle is an important psychological factor too, though, even if the times are equivalent.)