We obtained the current time point from std::chrono::system_clock. This STL clock class is the only one that can transform its time point values to a time structure that can be displayed as a human-readable time description string.

In order to print such time points, we implemented operator<< for output streams:

ostream& operator<<(ostream &os, 
                    const chrono::time_point<chrono::system_clock> &t)
{
    const auto tt   (chrono::system_clock::to_time_t(t));
    const auto loct (std::localtime(&tt));
    return os << put_time(loct, "%c");
}

What happens here first, is that we transform from chrono::time_point<chrono::system_clock> to std::time_t. Values of this type can be transformed to a local wall clock relevant time value, which we do with std::localtime. This function returns us a pointer to a converted value (don't worry about the maintenance of the memory behind this pointer; it is a static object not allocated on the heap), which we can now finally print.

The std::put_time function accepts such an object together with a time format string. "%c" displays a standard date-time string, such as Sun Mar 12 11:33:40 2017. We could also have written "%m/%d/%y"; then the program would have printed the time in the format, 03/12/17. The whole list of existing format string modifiers for time is very long, but it is nicely documented to its full extent in the online C++ reference.

Aside from printing, we also added time offsets to our time point. This is very easy because we can express time durations, such as 12 hours and 15 minutes as 12h + 15min. The chrono_literals namespace already provides handy type literals for hours (h), minutes (min), seconds (s), milliseconds (ms), microseconds (us), and nanoseconds (ns).

Adding such a duration value to a time point value creates a new time point value because these types have the right operator+ and operator- overloads, which is why it is so simple to add and display offsets in time.