The kernel has already been fixed, but userspace (glibc) is AFAICS still in progress. Glibc is going to do it in a similar fashion to large file support (LFS),

The kernel has already been fixed, but userspace (glibc) is AFAICS still in progress. Glibc is going to do it in a similar fashion to large file support (LFS), where if you define some particular macros you get the 64-bit time_t interfaces, otherwise you'll continue with the old 32-bit time_t. Similarly, existing binaries will continue to work, so in order to take advantage of 64-bit time_t you need to recompile (with those macros set, and fixing any resulting problems of course).