The tank has a radius of $2$m when initially filled and has an outlet of cross section $12$ cm2

Outlet flow as I calculated goes according to the law $V(t)=0.6\sqrt{2gh(t)}$.

Having found out the general description of the tank and the volume flowing out in time $dt Qdt=A v(t) ; Q=A v(t)$ in time $T$

After attempting further calculations, I do not know how to proceed to find the time taken to actually empty the tank