Took a Kaplan course during the same summer I took the MCAT. I was working a 40 hr per week internship at the same time so I didn't have a set schedule. I don't think I would recommend working full time while preparing for the MCAT especially if you only have 2.5 months. I liked that the prep course kinda forced me to at least attempt to keep with the material and it did cover all the content.
I second what
@efle mentions about really working on your weak areas. It can sometimes be oddly tempting to want to study the material you already know pretty well compared to working on your weak areas. Reviewing your practice exams to see what you are getting wrong and why you are getting it wrong is a huge part of preparing for the MCAT.
I had something similar (Kaplan course, 2.5 months, 40 hours a week job), but I actually recommend working full time because it provided a nice break (and money!)
But other than my job, it was almost all MCAT studying, with an occasional night out with friends (like, maybe 5 nights out total that summer). Granted, I procrastinate a lot when I study, so it was usually a combination of goofing off and studying. I just followed the Kaplan's recommended order of subjects, so I split each subject into 3 categories and alternated between subjects (Bio 1, Chem 1, Phys 1, Ochem 1, Bio 2, Chem 2 etc.). Eventually in my down time, I started memorizing various bio concepts via flash cards (stuff like circulation pathways etc.).
Good choice studying for it during the summer. I absolutely recommend you get it out of the way before the school year begins. I remember people in my summer prep class who scheduled their tests for January, which surprised me since I just wanted to get it out of the way.
I would recommend maybe prioritizing learning/re-learning the material during the first half of your studying, and prioritize practice tests during the second half. I started out with a 30 on my diagnostic test, and was pleased to see significant progress by the halfway point when I took my first practice test after that.