#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
inline int power(int a, int b) {
    int x = 1;
    while (b) {
        if (b & 1) x *= a;
        a *= a;
        b >>= 1;
    }
    return x;
}
 
 
const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;
 
//_ ***************************** START Below *******************************
 
 
 
 
vector<string> events;
 
string formatTime(int time){
	string hr = time/60 < 10 ? "0" + to_string(time/60) : to_string(time/60);
    string min = time%60 < 10 ? "0" +  to_string(time%60) : to_string(time%60);
 
    return hr + ":" + min;
}
 
void  consistency(int n, int k) {
	int m = 1440;
 
	vector<int> dif(m, 0);
 
	for(auto& e : events){
		stringstream str(e);
		string name, action, start, end;
		str >> name >> action >> start >> end;
 
		string startHr = start.substr(0, 2);
		string startMin = start.substr(3);
		string endHr = end.substr(0, 2);
		string endMin = end.substr(3);
 
		int startTime = stoi(startHr)*60 + stoi(startMin);
		int endTime = stoi(endHr)*60 + stoi(endMin);
 
		dif[startTime]++;
		if(endTime+1<m) dif[endTime+1]--;
	}
 
	for(int i=1; i<m; i++){
		dif[i] += dif[i-1];
	}
 
 
	int last = -1;
	for(int i=0; i<m; i++){
 
		if(dif[i] == 0 ){
			if(i-last >= k){
				cout << formatTime(last+1) << endl;
				return;
			}
 
		}
		else last = i;
	}
 
 
	cout << -1 << endl;
 
 
}
 
void solve() {
 
	int n, k;
    cin >> n  >> k;
 
    cin.ignore();
    events.resize(n); 
    for(int i=0; i<n; i++){
		string line;
    	getline(cin, line);
 
    	events[i] = line;
    }
 
	consistency(n, k);
}
 
 
 
 
 
int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
 
    int t = 1;
    cin >> t;
 
    cin.ignore(); 
 
    while (t--) {
        solve();
    }
 
    return 0;
}

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7
3 60
Alex sleep 00:00 08:00
Sam sleep 07:00 13:00
Alex lunch 12:30 13:59
3 60
Alex sleep 00:00 08:00
Sam sleep 07:00 13:00
Alex lunch 15:30 17:59
3 60
Alex sleep 01:01 08:00
Sam sleep 07:00 13:00
Alex lunch 15:30 17:59
3 60
Alex sleep 00:30 08:00
Sam sleep 07:00 13:00
Alex lunch 12:30 23:30
3 60
Alex sleep 00:30 08:00
Sam sleep 07:00 13:00
Alex lunch 12:30 23:59
1 1
Alex sleep 00:00 23:58
1 1
Alex sleep 00:00 23:59