A rigid disk rotates about a fixed axis through its center. Its angular position as a function of time \(t\) is given by \(\theta(t) = at^3 - bt^4\), where \(a\) and \(b\) are positive constants, \(\theta\) is in radians, and \(t\) is in seconds. Which of the following correctly pairs the non-zero time \(t\) at which the angular acceleration of the disk is zero with the direction of rotation of the disk at that instant?