How are you guys doing Quarter back Circle on Hitbox?

I’m a New 2D Fighter.

Using cammy and trying to do Cannon Spike ➡️⬇️↙️ and having trouble doing it consistently. I Can do Spiral Arrow decently. ⬇️↘️➡️. Not only that but I’m doing combo trials and I think I need to buffer it into moves and I’m too slow to hit the Cannon Spike. How do you guys hit your anti air so fast?

Also…what is the notation for this game? I only know Tekken