suggestion: Marathon setting for timed practice.
I don't like the reset time between practice sessions. If the timed practice had an increase in difficulty or a decrease in bonus time as challenges are completed people could try and see how many things they can get past. Maybe keep a high score or something.
I think this is a great idea! I also suggest being able to compete with friends! There are decreases in bonus time though. From what I've noticed, I think the amount of time you receive from answering questions depends on how quickly you answer them! Supporting you! :)