As a matter of ROUTINE, he spent 3 hours every school night on his studies, and more on the weekend.
That said, his freshmen classes were difficult because he took a good deal of dual enrollment classes in high school to knock out a lot of the core curriculum (English Comp, Sociology,Psychology, etc.). There wasn't a lot of room for "coasting" in his freshman schedule, because he had already earned the "easy" credits.
He had been told that the freshman engineering, programming, and calculus classes were always packed at the beginning of the semester, but that the herd would thin quickly. Whoever told him that was right.
My engineering class started with about 140 and graduated 38. Most of the weed-outs happened in Freshman Physics and Calc.
Kudos to your son for testing out of the easy stuff. I did the same (12? I think? English credits....).....left time for me to work on the important things.