Got it.
There is a maximum day number, but there is actually no real limit.
I set the number of days close to what we assumed was the maximum, that is 2,147,483,646. I did a dozen of runs on license IA2 (btw, I got an amazing time of 15'518, which kicks me up to 30th rank on GT3times ; perhaps because that has always been my favorite license to try this day increase stuff

)
The number first increased by 1 to reach the theoretical maximum of 2^31-1, then the next day was actually - 2,147,483,648 (which is - 2^31), and it kept increasing day after day.
Of course the 3 first digits of the number are not displayed on the screen, but I checked this in MK's.
So in case you fancy racing for 5,8 million game-years, your day counter will keep on clocking until 5,8 million game-years later you're back at day zero. By that time you'll be famous as the man with the two biggest thumbs of earth
@ kamikazefly : X-port or Sharkport users can use a little but excellent program made by a guy called MK, that allowed to do such crazy things like manually changing your money, you day counter, or even your cars. See in the hybrids section of the forum.
@ everybody : thread is answered to me. I hope I won't bother you again with one of these alien answers.
