Weekly Problem 6 - 2013
In one hour, the snail can reach points within $1$m of the corner at which it starts. So it can reach some of the points on the three faces which meet at that corner, but none of the points on the other three faces.
On each of the reachable faces, the oints which the snail can reach form a quarter of a circle of radius $1$m. So the required fraction is $\frac{\pi}{8}$.