I don't know - I graduated in three years without much difficulty, in engineering. Getting a head start with some AP work in high school was critical. Summer school may have been more limited, but it was also useful. Most important of all was to plan it in advance, and get all the prerequisite courses done in the right order.
To put it in perspective, consider a friend of mine who graduated from engineering from the India Institute of Technology. They required 240 credit hours to graduate, not the 120 that is required in the US. The credit hours were essentially the same as in the US, except that they also finished the entire textbook, whereas in the US, courses stopped wherever they were when the time ran out. To get those 240 hours done in five years required an average of 16 credit hours Fall, Spring, and Summer. Compared to that, my graduating in 3 years was no big deal, and I've never considered it a big deal, just a tuition saver.
I've said it before.
I'm a dinosaur.
So my experience in getting my engineering degrees is probably a lot different then yours.
Our idea of a computer was the old main frame in I believe Clippinger Hall.
There weren't any A.P. classes when I went to high school.
We also had very few "core" classes in college.
2 English classes,2 government or history classes and 1 P.E. class.
Everything else was either a required course or technical elective.
Schools did offer classes like calc.,chemistry,physics in the summer.
But those were all classes you had to take,during the school year, as a Freshman.
Most people were happy to graduate in 4 years.
Especially with the games they used to play with scheduling certian courses.