When in the heart cycle is the shock delivered during cardioversion?

Sync or non-sync. It depends whether it is synchronous or asynchronos. Synchronous is when the shock is delivered on the qrs portion of the heart cycle - it is when the heart depolarises. Asynchronous cardioversion can occur anywhere on the heart cycle.
Into the QRS. The shock is synchronized to the exact moment that the cardiac muscle is depolarized which corresponds to the qrs complex on the ekg.