A virus gone viral 2
To mitigate the rapid spread of this deadly virus some of the grid indices were left empty. How many microseconds does it take for all the organisms to be infected for the \(19\times 19\) grid shown below. were \(0\) means infected and \(1\) means normal and  means empty.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

Details and Assumptions
Explicit example, If the virus was spilled on a \(3\times 3\) grid.
\[\begin{pmatrix} 1 & 1 & 1 \\ 1 &  & 1 \\ 0 & 1 &  \end{pmatrix}\overset { 3\mu s }{ \longrightarrow } \begin{pmatrix} 1 & 1 & 1 \\ 0 &  & 1 \\ 0 & 0 &  \end{pmatrix}\overset { 3\mu s }{ \longrightarrow } \begin{pmatrix} 0 & 1 & 1 \\ 0 &  & 1 \\ 0 & 0 &  \end{pmatrix}\cdots \begin{pmatrix} 0 & 0 & 0 \\ 0 &  & 0 \\ 0 & 0 &  \end{pmatrix}\]
For a total of 15 microseconds.
The organism will quickly start infecting other organisms after being infected.