Примерно так
#include <iostream>
#include <chrono>
#include <ctime>
int main()
{
auto start = std::chrono::system_clock::now();
auto end = std::chrono::system_clock::now();
bool Cycle = true;
double SredSum=0;
std::time_t end_time;
double Entered = 0, count = 0;
setlocale(LC_ALL, "Russian");
std::cout. precision(5);
std::chrono::duration<double> elapsed_seconds = end - start;
do {
std::cin >> Entered;
if (std::cin. fail()){
Cycle = false;
break;
}
end = std::chrono::system_clock::now();
elapsed_seconds = end - start;
SredSum = ((SredSum * count) + Entered) / (count + 1. 0);
count++;
std::cout << "Среднее значение этих " << count << " чисел равно " << SredSum << std::endl;
if (elapsed_seconds. count() > 60) { Cycle = false; }
} while (Cycle);
}