If you try to avoid his apprehend reflexively you will fail, since by the time you see any telegraph, the move has actually already checked your hit box. You have to literally dodge it predictively , not reactively, you have to anticipate he MIGHT apprehend, and dodge away wether you see any telegraph or not. If you see Darius apprehend empty air, you did well. If you get grabbed anyway, you still did good because you properly anticipated his apprehend, just did not dodge before the move was cast and checked for hitboxes.
Tl:dr The move goes faster then the visual animation. You see Darius Apprehend, he actually already has apprehended. I hope this helps explain the mechanics ( I grabbed a renekton that had flashed away from me and my amumu jngler and I was awarded "LCS Hooks" I didn't know he'd flash, I hooked him because he used flash reflexively, if he had flashed sooner he'd have got away )