I advise summer school vs. lagging. I (a B-split) have done both, I did Physics II in summer school and I have lagged several classes. Speaking from experience, summer school is waaaaaay easier than lagging. When I did SS, it was I think three weeks about 6 hrs. per day of only the one class. We were entirely left alone by the regiment (Well, there was that one day CX2 tried to get us up for inspection and got several shoes thrown at him) and were able to focus on school work. When you are lagging Physics II, you are adding another 4.5 credits (if I remember right) on top of the 18 or so you are already taking. 22 or so credits is a killer schedule and is to be avoided at all costs if possible.
I did have to sail later than I really wanted, I didn't get off my ship until the first week of Jan, and got back to school 2 or 3 days late. I was on the 1/4 system and the splits were different so summer school may have a bigger impact on sea year now than it did then.