SDP required 9-12 hours a week on average (many more some weeks) spent on group projects. It would have been less if I'd been working alone. The hardest part is working in a distributed team with no leader - especially because lots of people take this as an "easy" intro course; of the 6 people I worked with, 4 of them were not comfortable being asked to do any programming. O_o
ML required ~25 hours a week on average; I spent close to 100 hours on it during weeks with projects due - fortunately there are only 3 projects. The lectures are longer than SDP, the projects are hard, and there are exams that you'll have no idea how to prepare for. You will love it anyway.
I am currently finishing up semester two of seven at UMUC's program. It's okay. Why am I in it? It's free for me.
I'm not sure what GT's masters program delivers, but UMUC's online program hasn't changed since it's inception (the 90s, I think). There are no online lectures and little guidance from professors. I read a text book, do exercises, submit assignments, take tests. I do like the structure and pace (two classes a semester), and I'll have a bachelors in computer science.
1. http://www.umuc.edu/academic-programs/bachelors-degrees/comp...