Changed to the following (note that the question remains about whether setting due dates should be optional):

You can set different dates for each action, and these dates can overlap. For example, you can allow students to submit responses starting on March 1, and require all responses to be submitted by March 7. You can allow students to begin peer and self assessments on March 1, when students can begin submitting responses responses, and allow them to continue peer and self assessments until March 14, a week after all responses are due.

If you don't specify dates, the deadline for all elements--responses, peer assessments, and self assessments--is the due date that you set for the subsection that contains the peer assessment. (**SP: We tell people that this is optional, but then include a warning about setting close due dates for response submissions and assessments. Does that mean this _shouldn't_ be optional?**)

  .. note:: We don't recommend that you use the same due date and time for response submissions and assessments. If a student submits a response immediately before the due date, other students will have very little time to assess the response before peer assessment closes. In this case, a student's response may not receive a score.