Checking whether a given timestamp is more than two weeks old
You're already using &lt;chrono&gt; (and just that), so you don't need &lt;ctime&gt;.  Including it anyway won't automatically allow compilation in pre-C++11 (if that was your intent here).

Also, since you're using uint64_t, you must include &lt;cstdint&gt; as well.
Each variable can be const since they're not being modified.  This would still be a good idea for ensuring const-correctness, even though the entire scope is within main().
The \ characters for line-continuations are useless here; the wrapping still works.
Since you're not needing to flush the buffer, std::endl should be replaced with "\n".  This may also give you a slight performance boost.
The "hello world" output can be shortened to a single-line ternary statement:

std::cout &lt;&lt; ((data_timestamp &lt; millis) ? "Hello" : "World");


Regarding this comparison: my tests give a signed/unsigned mismatch warning.  You have already given data_timestamp an unsigned type, so auto must be deducing a signed type for millis based on the function's return type.

One way to fix this could be by changing data_timestamp to a signed type such as int64_t, though &lt;chrono&gt; may offer more appropriate alternatives to help avoid uncertainty for this.
You don't need your own return 0 at the end of main().  The C++ standard should guarantee that the compiler will do this return for you since success is implied.