A) will be fine until 2038. I assume we have a lot of things that mashes time into an int or long. But such code is no worse off by virtue of the C library ty

A) will be fine until 2038. I assume we have a lot of things that mashes time into an int or long. But such code is no worse off by virtue of the C library types being fixed. B) -- manual calculation of size of structs instead of sizeof() -- yah, maybe it'll happen. I don't see much code this bad. If it's ever compiled on a different word length it's already been fixed. C) Perhaps. For the most part alignment improves when you have a wider time_t, but you could have people counting the number of 32 bit fields and then needing 16 byte alignment for SSE later. Again, for the most part this penalty has been paid by code compiling on amd64, etc.