The displacement of a body executing SHM is given by $x=Asin\left(2\pi t+\pi /3\right)$.The first time from $t=0$ when the velocity is maximum is 

$x=Asin\left(2\pi t+\frac{\pi }{3}\right)$
Velocity is maximum at mean position i.e. $x=0$
$$\begin{gathered} \Rightarrow sin\left(2\pi t+\frac{\pi }{3}\right)=0 \\ \Rightarrow \left(2\pi t+\frac{\pi }{3}\right)=0,\pi ,2\pi ,3\pi .... \end{gathered}$$
if we take $\left(2\pi t+\frac{\pi }{3}\right)=0$, time will come negative which is not possible. So we take $\left(2\pi t+\frac{\pi }{3}\right)=\pi$
$\Rightarrow t=\frac{1}{3}s=0.33s$
for other solutions, we will get higher values of time. but Since it is asking for the first time after $t=0$, the required solution will be $t=0.33s$