C++ Operator Overload plus + operator

#include <iostream>
#include <list>
#include <numeric>          //for accumulate()
using namespace std;
class airtime//  www  . j  a  v  a2s .  c  o  m
{
   private:
   int hours;            //0 to 23
   int minutes;          //0 to 59
   public:
   //default constructor
   airtime() : hours(0), minutes(0)
   {  }
   //2-arg constructor
   airtime(int h, int m) : hours(h), minutes(m)
   {  }
   void display() const  //output to screen
   { cout << hours << ':' << minutes; }
   void get()            //input from user
   {
      char dummy;
      cout << "\nEnter airtime (format 12:59): ";
      cin >> hours >> dummy >> minutes;
   }
   //overloaded + operator
   airtime operator + (const airtime right) const
   {                  //add members
   int temph = hours + right.hours;
   int tempm = minutes + right.minutes;
   if(tempm >= 60)    //check for carry
      { temph++; tempm -= 60; }
   return airtime(temph, tempm); //return sum
}
//overloaded == operator
bool operator == (const airtime& at2) const
{ return (hours == at2.hours) &&
(minutes == at2.minutes); }
//overloaded < operator
bool operator < (const airtime& at2) const
{ return (hours < at2.hours) ||
(hours == at2.hours && minutes < at2.minutes); }
//overloaded != operator
bool operator != (const airtime& at2) const
{ return !(*this==at2); }
//overloaded > operator
bool operator > (const airtime& at2) const
{ return !(*this<at2) && !(*this==at2); }
};  //end class airtime
int main()
{
    char answer;
    airtime temp, sum;
    list<airtime> airlist;   //list of airtimes
    do {                     //get airtimes from user
        temp.get();
        airlist.push_back(temp);
        cout << "Enter another (y/n)? ";
        cin >> answer;
    } while (answer != 'n');
    //sum all the airtimes
    sum = accumulate( airlist.begin(), airlist.end(),
    airtime(0, 0), plus<airtime>() );
    cout << "\nsum = ";
    sum.display();           //display sum
    cout << endl;
    return 0;
}