if you have a not-so-packed summer, i would take it this summer. if you have enough discipline to set aside time during the summer, you should be good. i took mine after my 2nd year of undergrad (i had taken orgo I and II, gen chem I and II, an intro bio class, and genetics) and although i did have to study a lot more on my own, i thought it was a good idea to do that instead of taking the dat the same summer as applying. but that's just me..