That's difficult to estimate because the course assignments are intertwined with doing work for your own blog, and because everyone will work at a different pace based on the other responsibilities in your life.
We counsel new students to allocate at least 10 hours per week for reading, study, writing and other course work. When you get into Module 3 you'll be spending most of your time outlining and writing posts, so your time will depend on how quickly you write. Expect your time to increase as you get further into the course, with more writing and outreach.