This is a version of our 4th grade class "final exam" on the times tables. The original whopper had 100 questions in 5 minutes, but since that requires redundant questions I reduced the number to 50.
I'm loathe to say this, but I think you have allotted too much time. I'm a slow typist, and usually hate the "beat the clock" type quizzes - but with this, I was able to take my time, make a few dumb mistakes, and still finish the quiz.
I wonder if all this people complaining about too much time are following the instructions and standing on their heads while they type. It's so much more challeging this way!
Considering that 82.6 % of quiz takers answer all the problems in the given time-frame and that you based it on 4th grade math, I would nominate this quiz for the Easy category.
it's more difficult to find the numbers on my keyboard than actually doing the math. Then again, i never learned how to type numbers without looking...