We highly recommend keeping the Submission Options setting at the Default of Open attempts are submitted automatically. 

Submission Options are set on the Timing screen for the assignment.

When Time Expires:  Submission Options - Explained

Open attempts are submitted automatically (Default)

This is our recommended setting. 

If a student has opened an attempt on an assignment, and does not actively Submit the assignment before the closing date, the attempt will auto-submit at the assignment's set Closing Date/Time.

All of our preset assignment templates are set to enter the Highest Grade earned among all attempts made into the gradebook, therefore, there is no risk to the student with the auto-submission setting.

This default setting also keeps students from contacting you at all hours if they realize they forgot to submit an assignment = fewer headaches for you!

If using custom templates or customized settings, consider the Grading Method (Highest grade, Average grade, First attempt, Last attempt) when using the auto-submit setting.

Grace Period

When selecting the There is a grace period when open attempts can be submitted, but no more questions answered option, students will be given the set amount of time, beyond the assignment's Closing Date/Time, to actively Submit the assignment. 

THIS DOES NOT ALLOW THE STUDENT TO CONTINUE WORKING ON THE ASSIGNMENT PAST THE CLOSING DATE/TIME.

Once selected, check the Enable box to open the Submission grace period fields and set to the desired time frame.

This setting only allows the student extra time to actively Submit the assignment. 

WARNING!  If the assignment is not Submitted before the Grace Period ends, the student will not receive a grade in the gradebook.

Require On-Time Submission

When selecting the Attempts must be submitted before time expires, or they are not counted option, students are required to actively Submit the assignment by the assignment's Closing Date/Time.

WARNING!  If the assignment is not Submitted before the Closing Date/Time, the student will not receive a grade in the gradebook.