I finished the A and B licences fairly quickly after getting the game, they're good for the basic race skills. IB didn't take me long either, but IA took me ages. After that, I had access to almost every race in the game, so I didn't even attempt S until I'd managed a fair chunk of beginner and amateur, and had a crack at professional.
After finishing beginner league completely and most of amateur league, I gave the game a rest for a few months while I went to uni etc. I just got back into it a month or so ago, and the first thing I tried was the S licence. I finished all 8 races with bronze in about 2 days, and I kind of sat there awestruck for another day or so after that.
Since then I've been significantly improving my speeds and times, and I can handle quite powerful cars now with a reasonable degree of finesse, where before I was well acquainted with almost every sand trap in the game.
The moral of the story? Sometimes it's better to leave the whole thing behind for a little while and focus on something else. Spending a week trying the same test is definitely not conducive to improving your times.
And caffeine doesn't help! Trust me! It just makes you twitchier and more prone to controller abuse
