C.P.
We just made the same trip about a month ago. My son was 9 months old. We chose to leave in the late afternoon during his afternoon nap (around 3). He slept for about 2 1/2 hrs. When he woke up, he played for about 30 min before getting antsy. By this time it was around 6:00 and we stopped for dinner. This way he could get out of the carseat and play for about an hour. Got back on the road around 7ish and he played (just with his rattlers) for about 30 min before drifting off to sleep. His normal bedtime is 7:30/ 8:00 so he was out for the night. My husband and I were tired so we stopped about 1:00 am and got a hotel room. When we got up the next morning, we only had 3 hrs left. I woke my son up an hour earlier than normal. We had breakfast and were on the road for his normal morning nap. He slept for all but 30 min. By that time, we were by the beach and could put the windows down and he was a happy camper.