  In 2-neighborhood bootstrap percolation on a graph $G$, an infection spreads
according to the following deterministic rule: infected vertices of $G$ remain
infected forever and in consecutive rounds healthy vertices with at least two
already infected neighbors become infected. Percolation occurs if eventually
every vertex is infected. The maximum time $t(G)$ is the maximum number of
rounds needed to eventually infect the entire vertex set. In 2013, it was
proved by Benevides et al \cite{eurocomb13} that $t(G)$ is NP-hard for planar
graphs and that deciding whether $t(G)\geq k$ is polynomial time solvable for
$k\leq 2$, but is NP-complete for $k\geq 4$. They left two open problems about
the complexity for $k=3$ and for planar bipartite graphs. In 2014, we solved
the first problem\cite{wg2014}. In this paper, we solve the second one by
proving that $t(G)$ is NP-complete even in grid graphs with maximum degree 3.
We also prove that $t(G)$ is polynomial time solvable for solid grid graphs
with maximum degree 3. Moreover, we prove that the percolation time problem is
W[1]-hard on the treewidth of the graph, but it is fixed parameter tractable
with parameters treewidth$+k$ and maxdegree$+k$.
