E.F.
I did my master's degree online part time, over 3 years. For me, it wasn't so much the online part (which took about 45 minutes a week), but the volumes and volumes of reading I had to do, to prepare for the online tutorial and get through the reading list. I did it while working full-time, and later, when I quit my job to stay home with my baby, I read while he napped, every evening after he fell asleep and on weekends while my husband took my son to the park. It was hard (I'd hear my husband laughing at funny movies in another room and really wanted to join him), but exhilarating, too. I found it stimulating to have big concepts to chew on in the evenings. It helped my transition from professional career gal to full time mommy. Hopefully, it will help my transition back into the work force, too. If I added it up, I would say I studied 10-15 hours a week for a part-time course and more as exams approached.
Good luck with your program!
ps - I have some complaints about the online system. I've done a lot of post-secondary education and there is no replacing the educational value of bouncing ideas off your peers and learning through discussion and debate. I found that to be missing in the online system. I would suggest getting a 'study group' of a few people in your class so you can work on problems, ask each other questions and share ideas as you progress.