Matrix - find the time required so that all oranges rot - python

Given a matrix of dimension m*n where each cell in the matrix can have values 0, 1 or 2 which has the following meaning:

0: Empty cell

1: Cells have fresh oranges

2: Cells have rotten oranges

So we have to determine what is the minimum time required so that all the oranges become rotten. A rotten orange at index [i, j] can rot other fresh orange at indexes [i-1, j], [i+1, j], [i, j-1], [i, j+1] (up, down, left and right). If it is impossible to rot every orange then simply return -1.