I took mine in the beginning of June after my Junior year and that worked out well time-wise. Taking them after sophomore year would be nice because Ochem would still be more fresh and then that would be less stress for you during Junior year. But all in all ideally you want them done by the May or June after your Junior year so that you can be an early applicant. All in all though take them when you are prepared and can give yourself ample time to prepare because anyone can do well on it if they study enough. Too late is probably September or October of the year you are applying. Thats my DAT rant, hope it was helpful