Hi Rosalynne Whitaker-Heck,
If students are popping in and out of the sections in any order throughout the semester, then you're right, do not put in due dates for those parts. Is there anything that they have to submit each week to show they are making progress?
I would suggest having a separate category of assignments for Status Updates or Check-ins whatever, that will have weekly due dates and the students can write a quick report of which section they worked on during that week.
Another alternative, is to put to-do dates on the explanation pages and then it will show up on the Student To-Do list. But not in the Syllabus.
How do I create a new page in a course?

You can add the page to the student to-do list by selecting the Add to student to-do checkbox [2]. When you add a page to the student to-do, the to-do displays in the student's to-do list as well as the in the course calendar and modules.
Hope this alternative helps,
Cheers - Shar 
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