An assignment is late if it is completed (and the Reader notified) after 11:59 p.m. of the due date.
If--this should never happen, but just if--you are late, you will be assessed a 5% penalty the first late day, and 10%-per-day penalty after that in your grade for that assignment. (Since e-mail is available every day, each of the seven days of the week counts as one day.)