Goodluck with the homeschooling MON!
DD does G3. I would say that the amount of time it takes to do the assignments depends a great deal on how fast a reader you are and how much depth you like. DD is taking the class ungraded (as recommended by Jaime.) She is pretty independent with it.
The webinars are done through Elluminate. For best results, use a headset with a microphone. The instructor can activate a student's microphone to let the student speak. Everyone hears what other people say. Responses can also be typed or drawn on the virtual blackboard. Kids can raise their hands to be called on or ask a question. The interactive class takes 1hr/wk.
There are also forums which are used for assignments and others for social interaction. Those you can access as much or as little as you like. Nobody makes you do assignments, and there are no tests.
DD enjoys it, and we plan to sign up for more classes in the future. Also, check out Athena's Advanced Academy which uses a similar format.