If i have q query [start, end] in the graph. How to check whether:

the length of start to end can be arbitrarily negative length?

0  floydWarshall(matrix, n) // RUN THE FLOYD WARSHALL ALGORITHM
1  FOR (start, end) in q:
2  check = false
2  while(start != end)
3     start = Next(start)
4     if (dist[start][start] < 0)
5          check = true, break
6  if check == true
7     return "Negative Loop here"

I try the code like above and get Time limit because I have a while loop inside which is to find negative loop in the path from start to end.

Can you help me find another method?