Consider a student who has only one correct answer but submits his test on time, and another who has all the correct answers but submits his test after the deadline. The first student gets say 1/50 for comprehension and 50/50 for time, and the second
student gets 50/50 for comprehension and 0/50 for time. Thus, the first student gets a total of 51/100 even if he has virtually no knowledge of the subject, while the second gets only 50/100 while he mastered the subject but answers simply more slowly.
With your grading system, regardless of his level of comprehension, no student would benefit from continuing his quiz after the deadline because, in any case, his mark would be lower than he would obtain if he submitted his test in time.
Why would you want to set up such a grading system?