They already hit August and March, if they're confident enough they may go for a winter or summer release for the third if it's a big spectacle.
If Paramount gets a big hit film on their hands, they usually stick to the same seasonal release for sequels. Take
Paranormal Activity and the
Star Trek reboot, for example. Originally,
G.I. Joe 2 was supposed to hit the same August weekend the first pic did last year, but was moved up to June (thanks to
Star Trek 2 not going into production yet) and then pushed back to late March 2013 for the 3D conversion.
They ought to take a leaf out of Universal's switcheroo strategy for their
Fast & Furious franchise. Two of the top 3 grossing movies in that franchise so far have been April releases, thanks to lack of competition and good marketing. Then when the franchise regained its popularity, that's when it moved back to summertime.
Since
G.I. Joe: Retaliation didn't get that huge uptick
Fast Five did, Paramount could probably do gangbusters by giving
G.I. Joe 3 an early spring (February-April) or even fall (October-November) release. Then when that's successful, spring for a prime summer release date for a fourth pic.