std::filesystem::file_time_type(3)

NAME
std::filesystem::file_time_type - std::filesystem::file_time_type

Synopsis
   Defined in header <filesystem>
   using file_time_type = std::chrono::time_point</*trivial-clock*/>; (since C++17)
                        (until C++20)
   using file_time_type = (since C++20)
   std::chrono::time_point<std::chrono::file_clock>;
   Represents file time.
   trivial-clock is an implementation-defined type that satisfies
   TrivialClock and is sufficient to represent the resolution and range (until C++20)
   of the file time values offered by the filesystem.

Example
// Run this code
 #include <chrono>
 #include <filesystem>
 #include <format>
 #include <fstream>
 #include <iostream>
 using namespace std::chrono_literals;
 int main()
 {
     auto p = std::filesystem::temp_directory_path() / "example.bin";
     std::ofstream(p.c_str()).put('a'); // create file
     std::filesystem::file_time_type ftime = std::filesystem::last_write_time(p);
     std::cout << std::format("File write time is {}\n", ftime);
     std::filesystem::last_write_time(p, ftime + 1h); // move file write time 1 hour to the future
     ftime = std::filesystem::last_write_time(p); // read back from the filesystem
     std::cout << std::format("File write time is {}\n", ftime);
     std::filesystem::remove(p);
 }

Possible output:
 File write time is Sun May 9 23:29:58 2021
 File write time is Mon May 10 00:29:58 2021

See also
   last_write_time gets or sets the time of the last data modification
   (C++17) (function)