std::chrono::time_point

#include <algorithm>
#include <chrono>
#include <ctime>
#include <iomanip>
#include <iostream>

void slow_motion()
{
    static int a[] {1,2,3,4,5,6,7,8,9,10,11,12};
    //  (13) == 12! :
    while (std::ranges::next_permutation(a).found) { }
}

int main()
{
    using namespace std::literals; //   , 
                                   // 24h, 1ms, 1s.
    const std::chrono::time_point<std::chrono::system_clock> now =
        std::chrono::system_clock::now();

    const std::time_t t_c = std::chrono::system_clock::to_time_t(now - 24h);
    std::cout << "24     "
              << std::put_time(std::localtime(&t_c), "%F %T.\n") << std::flush;

    const std::chrono::time_point<std::chrono::steady_clock> start =
        std::chrono::steady_clock::now();

    std::cout << "  : \n"
              << "  : " << now.time_since_epoch() << "\n"
              << "  : " << start.time_since_epoch() << "\n";

    slow_motion();

    const auto end = std::chrono::steady_clock::now();
    std::cout
      << "   "
      << std::chrono::duration_cast<std::chrono::microseconds>(end - start).count()
      << "  "
      << (end - start) / 1ms << "  " //   ,  ,
      << (end - start) / 1s << ".\n";  //      
                                        // 
}