Rice University has developed a nice workload estimator that you might consider using for your course. It is available at https://cte.rice.edu/workload.  

From the Center for Teaching Excellence at Rice:  Somewhat surprisingly, there is very little research about the amount of time it takes the average college student to complete common academic tasks. We have self-reported estimates of how much total time they spend on academic work outside of class (12-15 hours), but we don’t know much about the quality and quantity of the work that is produced in that time frame (let alone how the time is allocated to different tasks). We also know quite a bit about how students tackle common academic tasks, but those studies rarely ask students to report on how long it takes them to complete the task (whether reading a book, writing a paper, or studying for an exam). The testing literature provides some clues (because valid instrument design depends on data about the average speed of test takers), but it’s tough to generalize from the experience of taking high-stakes, timed tests to the experience of working on an assignment in the comfort of your dorm. And while there is a sizable literature on reading, the nature and purpose of the reading tasks in these experiments are also quite different from what students typically encounter in college.