It all depends on the spec of your machine, the amount of leagues and in my case the amount of players you load up.
I have a high end PC, very capable and recently I started a brand new game with 30 odd leagues in 17 odd countries, huge database and i loaded all the players from about 30 odd countries.
My season would take me a solid 36 odd hours.
Started again, did not load all these players, played with a huge database and about 23 leagues, my season now takes about 8 hours.
Depends on all those factors I reckon.