Harmonize does support individual due dates for students. After you've adjusted a student's due date in Canvas, Harmonize will automatically pick up the new date once the student opens the discussion. For milestones, the same date offsets will be applied to the student's new due date and SpeedGrader submissions will be adjusted accordingly as well. As an instructor, you will continue to see the primary due date set for everyone else, but the individual students will see the new due dates reflected in their view of Harmonize.