Deadline reports that Paramount's internal projections are indicating they could make $150 million at the US box office over the five day 4th of July weekend. In a desire to exceed or surpass that number they have decided to announce "an exclusive 3D and IMAX engagement" for Tuesday, June 28th at 9PM. Paramount had previously bumped the release date from July 1st to June 29th. They also did this for Super 8.
The exact details are unknown the time frame allows time for theatres to still do 12:01AM showings. If I recall correctly, Paramount did the same thing for Revenge of the Fallen. Personally I have my tickets for the 7PM showing of The Lord of the Rings: Return of the King Extended Edition showing and the 12:01am Transformers: Dark of the Moon in IMAX 3D so it has no impact on my movie plans for that day.