Actually, it wouldn't change anything since add/sub are the same for signed (2s comp) and unsigned ints and C will happily let you assign a signed literal to an

Actually, it wouldn't change anything since add/sub are the same for signed (2s comp) and unsigned ints and C will happily let you assign a signed literal to an unsigned variable. You would just get some compiler warnings and maybe break the rare piece of code that multiplies negative time deltas. What you have to fix are the operations that convert between time_t and some other representation and those are not going care about the data type.