Technically, you have not submitted the assessment and that will be logged in the system. You can still submit it, of course, providing you are within the permitted late period, it will be accepted as a late submission. Then you could make a PMC/EC application to ask that the penalty be lifted due to technical problems - but you would need supporting evidence. BTW where I am, 4pm is classed as LATE, the work has to be sbmitted by 3:59.