No, it's not too early if you've already finished your core sciences. In fact, it's probably better to plan ahead and spend the summer studying and take it afterwards. That way, if for some reason it doesn't go well, you have more than enough time to re-do it. I wish I had planned ahead and taken it last summer when I wasn't doing anything, because now I have to stress about getting all my application materials together while studying for the DAT at the same time :/