Just some advice from my experience in 4th year. Some rotations you may only work about 40 hours/week. But then I had some rotations where I was onsite 60+ hours/week. Then I spent time at home working on projects and presentations. I worked 3 days/week P1-P3, but I only worked once a month during 4th year. My time became very precious, and I didn't want to exhaust myself to the point that I would hate the profession.
So don't plan on working too much during 4th year. If you have extra time and you can work, then great...go for it.