I dont play more than an hour to improve my time. if my time is going to improve, it improves in one hour. if i play more than an hour, it is pure waste of time. I played 1 hours with normal car and shaved off about 0.8s to 1:49.8xx and 1:37.6xx tuned. before i play, I always watch a replay of GTP_timeattack or GTP_dramakyd.