That is a great question! Currently, there is not a way to prevent students from editing a WikiProject after the due date, however, there is a workaround to restrict access to students. I am providing a link below to an article that will provide steps to restricting the access. Once you open the article locate the last section titled, Due Dates.
If you have additional questions, please let me know and I will be happy to help. Thank you for reaching out for assistance through the Community!