Excellent! As you can see from the figure itself, at \(t = 4\) s, the slope is the largest. At \(t = 1\) s, the slope is the flattest. As time increases, it grows steeper and steeper.
Now, look at ball actually falling. When do you think the ball will have the maximum velocity? (Again, ignore the negative sign of the velocity.)

\(t = 1 \, \mathrm{s}\)

\(t = 2 \, \mathrm{s}\)

\(t = 3 \, \mathrm{s}\)

\(t = 4 \, \mathrm{s}\)