If you have a student that needs extra time to complete an assignment (e.g., joined the course late, excused absence, etc), you can override the deadline for that student for a particular assignment. To do this:

  1. Navigate to Course Setup > Readings.
  2. Click to highlight the assignment under the Assignments panel.
  3. Click the clock icon in the toolbar to view and edit per-student deadlines.
  4. Click the pencil icon next to a student's deadline to change the deadline for that student.

You can even extend deadlines after the fact; Perusall will always recalculate scores to make them consistent with your current assignment settings.