When you submit an assignment, Moodle sends a message to both you and me that contains the name of the assignment along with the time/date of the submission. You should retain these messages.
When I grade an assignment, Moodle will send you a note that I have done so. It will also suggest that an evaluation of your work has been submitted. This is not always the case. If I don’t create a response, you receive only the grade.
This receipt will indicate the time the upload finished.
My system keeps a copy of these receipts.