Shoot for Aug but don't take it until you're ready, if you can't take it during your program shoot for the end of June so you have some extra crunch time to extend into if need be. I was retaking it and my deadline hit and I had felt ready for the sciences but neglected the non science sections and time ran out, I ended up doing much better in science and much worse in the other sections prompting some interview questions. Lesson is be fairly ready for it all before you sit down to retake it. If you aren't push it off and keep it as your top priority. Also on a side note FYI many schools won't consider you if you are in the middle of a masters program so do some research on that if you that is indeed what you are doing.