The time to go from mean position to $x = A/2$ is $T/12$, while the time from $A/2$ to $A$ is $T/6$ (twice as long). From mean to $A/\sqrt{2}$ takes $T/8$. Students often assume equal distances take equal times in SHM — this is wrong because the velocity is not constant. The particle spends more time near the extremes (where it slows down) and less time near the mean (where it speeds up). Use $x = A\sin(\omega t)$ and solve for $t$ to find the time for any displacement.