The Apprentice Program takes a lot of time. Besides writing 8 hubs a month, you have lessons to go through (about 1-2 hours a month). You also want to participate in the forum for your group - reading their hubs and answering questions, getting feedback and using it, maybe researching more than you used to. The hubs take a little longer to write than usual because you are trying to make them the best they can be, and incorporating the things you learned each month.
I can't tell you how much time that will take, because I don't know how much time it takes you now to make a hub, and how much time you spend in the community, etc., but it can take a lot of time if you let it. You can also do the minimum and not get as much from the program. I think you could easily spend 8-20 hours a week.
If you decide you are not ready, you might consider doing your own course by reading up on the learning center articles that follow the topics that will be discussed in the program - attributing images, search engine optimization, building a brand, etc.