Currently, if a student submits an assessment at what appears to be the exact due date and time, they are penalised (unless the individual penalty is overridden by staff). So far as the student is aware (and staff for that matter) the assessment is on time.
For example, the below shows that a student submitted a paper on May 4 at 1700hrs. This is the due day and time, but a late penalty has been applied (per the late policy). After calling Canvas support, I found out that the student actually submitted at 17:00:04... four seconds after the due date. However, this information is not visible to the students or staff, so for the student it looks like the a penalty has been applied unfairly. For staff, they cannot verify if it is a glitch, or the student has submitted within that one-minute time frame. Many students submit up until the last minute, so this is something that is bound to happen often.
I suggest one of the following changes are made to fix this issue:
Allow seconds to be entered in the assessment due date and time (i.e. 4 May 2018 at 17:00:59 etc.); or
Display the submission date including seconds, not just down to the minute (visible to students and staff); or
Have a field that lists how late the assessment is (our previous system did this, it would state '1 day 20 hours late' etc.).