StarCraft 2 season five is drawing to a close. The leaderboards will go into lockdown on Tuesday February 14, so you'll want to make that final push for the top spot pretty soon. You'll still be able to play during the lock down of course, and your wins and losses will be tracked, but your wins won't affect your final season five placement.
A post on Battle.net says that season six will start in the week starting February 20. "During the Season 5 lock, you can no longer be promoted or demoted out of your current league or division, and your bonus pool will stop growing," say Blizzard, BUT, "the hidden ratings used to determine promotions and demotions will continue to update during the Season 5 lock and be used for matchmaking purposes."
"This means that if you play significantly better or worse than your assigned league at the time of the lock, your league may change when Season 6 begins." A good time to get cracking if you're looking for that elusive league promotion.