Unless I'm missing something here, you can drop the cast to unsigned long long: time64_t is always 'long long' and won't cause a warning here.
We only need a cast like this when printing the members of 'struct timespec64', since that can be either 'long long' or 'long', when it is defined as an alias for timespec.
You are right. I think I had timespec64 on my mind when I added this cast. I will update the series with the casts removed.