There's more...

Take account of the fact that we are returning a blank direction when the time is negative; it means that the speed is not sufficient. One way to overcome this is to define a function that tests different speeds and then shoot the projectile.

Another relevant improvement is to add an extra parameter of the type bool for those cases when we have two valid times (which means two possible arcs), and we need to shoot over an obstacle such as a wall:

if (isWall) 
    time = Mathf.Max(time0, time1); 
else 
    time = Mathf.Min(time0, time1);