Although we have not had this confirmed by Paramount, these dates seem to line-up and make some sense. Take it for what it's worth:

Hey Guys! My uncle's brother works for Michael bay, it's funny becuase his name is Michael too. He gave me the release dates for upcoming trailers and TV Spots for the third and final installment of Transformers.

ANNOUNCEMENT TRAILER - DECEMBER 8, 2010
SUPERBOWL TV SPOT "DARK" - FEBRUARY 6, 2011
DAYTONA TV SPOT "NASCAR" - FEBRUARY 19, 2011
TEASER TRAILER - MARCH 25, 2011
REELZ TV SPOT "AUTOBOTS" - APRIL 3, 2011
MTV TV SPOT "MOON" - APRIL 21, 2011
THEATRICAL TRAILER - MAY 5, 2011
NICK TV SPOT "INVADE" - JUNE 13, 2011
MOVIE RELEASE IN 3D - JULY 1, 2011
5 MINUTE SNEAK PEEK on NICKELODEON - July 25, 2011
DVD TV SPOT 1 - SEPTEMBER 8, 2011
DVD TV SPOT 2 - SEPTEMBER 23, 2011
DVD/BLU-RAY RELEASE - OCTOBER 4, 2011