std::this_thread::sleep_for(5s); 

std::map<int, int> mp;
decltype(mp)::mapped_type t;

#include <iostream>
#include <chrono>
#include <thread>
#include <future>
#include <map>
using namespace std::chrono;
using namespace std::chrono_literals;
using namespace std;

int find_answer_to_the_ultimate_question_of_life()
{
    std::map<int, int> mp;
    decltype(mp)::mapped_type t; // <-- unexpected token t

    //Поиск ответа
    std::this_thread::sleep_for(5s); //  <-- unexpected token ';' got '<error>'
    return 42;
}

int main()
{

    std::future<int> f = std::async(std::launch::async,
                                    find_answer_to_the_ultimate_question_of_life);

    if (f.wait_for(5500ms) == std::future_status::ready ) <-- unexpected token ')' got '<error>'
        std::cout << "Answer is: " << f.get() << "\n";
    else
        std::cout << "Can't wait anymore\n";
    return 0;
}

TEMPLATE = app
CONFIG += console
CONFIG += c++14

SOURCES += main.cpp 

QMAKE_CXXFLAGS=-std=c++14