输入采用scanf("%d:%d", &time.hour, &time.minute)会比较省事 

#include<iostream>
#include<cstdio>
#include<vector>
using namespace std;
typedef struct Node{
	int hour;
	int minute;
	int endh;
	int endm;
}node;
int main()
{
	int N;
	cin >> N;
	int starth = 13, startm = 15;
	vector<node> vtime;
	for (int i = 0; i < N; i++) {
		node time;
		scanf("%d:%d", &time.hour, &time.minute);
		int carry = 0;
		time.endm = startm + time.minute;
		if (time.endm >= 60) {
			carry = 1;
			time.endm -= 60;
		}
		time.endh = (starth + time.hour + carry) % 24;
		vtime.push_back(time);
	}
	for (int i = 0; i < N; i++) {
		cout << vtime[i].endh << ":" << vtime[i].endm << endl;
	}
	return 0;
}