Season 4 Now Locked
Attention, StarCraft II ladder competitors! Season 4 is now locked.
At the end of each ladder season, leagues are “locked,” which means players can no longer be promoted or demoted out of their current league or division, and bonus pools will stop growing. That’s no reason to quit playing: even after leagues are locked, players will still be able to play out their remaining bonus pool and compete for standing within their divisions until the season ends one week later. The matchmaking skill ratings which determine league promotion and demotion will also continue to update during the lock, so games played during the lock still count toward Season 5 league placement.
Now that the lock is in effect, Season 4 will soon come to an end. We’ll be turning over to Season 5 during the week of December 19, and the Grandmaster League will start one week following the season roll. Season milestone rewards will be awarded and bonus pools will reset with the beginning of the new season. Hidden skill ratings used for matchmaking and league placement will carry over from the previous season, though, so players who have completed placement matches in a previous season will only need to play one new placement match after Season 5 starts.

no it start in this week so could be in 3 days
if you look at the league promotion post linked in the article it says this: "One way to almost guarantee a promotion by next season is to earn the number of division ladder points given in the corresponding table entry below by December 13, in anticipation of a December 20 season roll.*"
I think that hints evidence to the Dec 20th mark. =3
If Rank 1 has 800 points after two months, and you only have 150-400....Doesnt it make logical sense that with a longer season, the disparity (in percentage) would be the same? You'd still only play on the weekends and get another 200 points or something, but #1 keeps playing every day and will be up to 1000+ points. The ratio is the same, don't fool yourselves. Find time to play more. Simple as that.
seasons are way too short.
Tournaments or league play!
C'mon Blizzard