it does make it longer but not much, it doesnt really effect your acceleration so this is how it works.
1 each tooth extra on your front sproket equates to 2.17 teeth less on the back. now with the removal of another 4 teeth on the back sproket this equals 6.17 teeth which is approximatly 15% more efficient. when you think about it, this is quite a bit more but i dont know how much longer it will make his 1st, it may be like 2.6 seconds but not much more than that but realistically you dont want first to be too big otherwise you will lose top end acceleration.
Cheers, Tony.