std::chrono::time_of_day<Duration>::time_of_day
From cppreference.com
                    
                                        
                    < cpp | chrono | time of day
                    
                                                            
                    |   time_of_day() = default;  | 
(1) | |
|   explicit constexpr time_of_day(precision since_midnight) noexcept;  | 
(2) | |
Constructs a time_of_day object.
1) Default constructor leaves the object uninitialized.
2) Constructs a 
time_of_day object in 24 hour format corresponding to since_midnight after 00:00:00. As applicable:
hours()returns the integral number of hourssince_midnightis after 00:00:00.minutes()returns the integral number of minutessince_midnightis after(00:00:00 + hours()).seconds()returns the integral number of secondssince_midnightis after(00:00:00 + hours() + minutes()).subseconds()returns the integral number of fractional secondssince_midnightis after(00:00:00 + hours() + minutes() + seconds()).