How do I argue the idiocy of turnin.com's time restriction?

I don't have a major problem with turnitin.com, but I do have a problem with having to turn it in to the website by a certain time. why is this necessary, does it matter if i turn it in a little late? does it suddenly become plagiarized? of course not! so then why does my teacher refuse to give me an accurate grade for my work, based soley on this fact? and how do i explain this stupidity?