A submersible's dive is modeled by a quadratic function $D(t)$, where $D(t)$ is the depth in meters below the surface and $t$ is the time in minutes. The submersible starts its dive from the surface ($D(0)=0$). It reaches its maximum depth of $450$ meters after $15$ minutes. At what other time, to the nearest tenth of a minute, was the submersible at a depth of $200$ meters?