A rocket is launched vertically up, and its height above the ground is given by the function $h\left(t\right)=400t-50t^2$, where $h$ is in meters and $t$ is in seconds. The graph below shows $h\left(t\right)$ along with its velocity function $v\left(t\right)=\frac{dh}{dt}$ and the acceleration function $a\left(t\right)=\frac{d^{2}h}{d{t}^2}$ for the time interval $0\le t\le 8$ $\text{s}$.

Using the graph, determine the time when the rocket changes direction.