Spread Spree

You have a grid with $N$ rows and $M$ columns. The cell at the intersection of the $i$-th row and $j$-th column is denoted $(i, j)$. Initially, every cell of the grid is white. You will choose **exactly one** cell of the grid and color it black. This coloring then spreads to the rest of the grid — every second, each black cell causes all its neighbors (horizontal, vertical, and diagonal) to als