A typical semester long college course nominally has a workload of about 12 hours per week, including in-class and out-of-class time.
So a high school AP course that covers a semester’s worth of college course material over a year (e.g. psychology, statistics) should have a workload of about 6 hours per week. If the in-class time is about 4 hours per week, it should have about 2 hours per week of reading, homework, and studying outside of class.
But a high school AP course that covers two semesters’ worth of college course material over a year (e.g. calculus BC) should have a workload of about 12 hours per week. If the in-class time is about 4 hours per week, it should have about 8 hours per week of reading, homework, and studying outside of class.
However, actual time spent on college courses is somewhat less than nominal for most (lab courses, computer science courses with programming, art studio, and music performance are commonly among the exceptions), so actual time spent on AP courses covering the same material may be somewhat less than nominal-equivalent as well.
There can also be variation in that some instructors can make the course more or less work than typical.