Tom,

Ahh, the problems of an asynchronous online course! There aren't the "natural" limits of a classroom based course, where interaction is limited to scheduled periods.
I'm afraid there's not much we can do about that, other than to note that I certainly don't expect everyone to log in twice a day, or even every day. Like many things, the more you can put into it, the more you will get out of it, but also like many things, you have to find your own balance. Some students will be able to only "join the conversation" a couple of times per section, others will jump in daily or more often. Both are okay.

Jim