Major releases of LLVM -- along with sub-projects like Clang -- release every half-year. With LLVM 3.4 having been released in January, it puts the 3.4 release mid-way in the year.
LLVM developer Bill Wendling confirmed this week that the target release month for LLVM/Clang 3.5 is August while the organized testing process will begin in July. The precise LLVM 3.5 release schedule is still to be decided. Meanwhile, LLVM 3.4 point releases have started coming and more are on the way.
So far there's some LLVM 3.5 changes queued up, including the new/converged 64-bit ARM back-end, while much more work is still forthcoming.