How do I know when a student submitted an assignment after the due date?

You can easily see when students submit their assignments (and if they submit them late) with timestamps.

For a Library Lesson: go to the Assignment Report for a particular text and scroll down to the students' names. There, you will see a clock icon between the students' name and total score. Hover your mouse over the icon to view the timestamp.

If a student has submitted an assignment after the due date, it will read "Late" in red lettering in the timestamp. 

For a 360 Lesson: go to the Assignment Report and scroll down to the Overall Scores table. There, you will see a clock icon next to the students' score under the Total Score column on the far right of the table. Hover your mouse over the icon to view the timestamp. If a student has submitted an assignment after the due date, you will see an exclamation point instead of a clock, and it will read "Late" in red lettering in the timestamp.