One thing that stood out for me as well was that someone else indicated that, in general, the only requirements were the exams. Most of the engineering classes I took had weekly problem sets that, yes, took at least a solid evening to do.

The way my undergraduate did credits was the (theoretical) number of hours a week they took between lectures, lab, recitation, and study/problem sets. Typical classes added up to 12 with usually 4 hours of the first 2 categories and 8 hours of the last. Classes varied but that wasn't too far off for the typical class. (Though there were some real time sink outliers.)