Sorting an array of time of day values

I have to save into an array the hour format, example: 2:00AM, 3:45PM, 1:45AM, 12:56PM, etc., and next sort by the earliest hour, example: 1:45AM, 2:00AM, 12:56PM, 3:45PM. I only made the sort by the number but I don't really know how to sort by the "AM" or "PM" format.

#include <iostream>
#include <vector>
#include <algorithm> 

using namespace std;

int main(){

int cont = 0;

int num;

cout << "Introduce length of array: " << endl;

cin >> num; 

string ar[num];

string hour;

cout << "Introduce hour (hh:mm AM or PM) example: 02:11PM" << endl;
    
for(int i = 0; i < num; i++)
{
    cin >> hour;
    ar[i] = hour;
        
}

sort(ar, ar + num);


cout << cont << endl;

for(int i = 0; i < num; i++)
{
    cout << ar[i] << endl;
}

}