The moment Zeus got back to Mount Olympus, he watched John through a scrying crystal. He had seen that John had been working on his magic, though he was a bit surprised that he seemed to be fairly advanced.

He could step in any time if he needed to to stop John if he took a step out of line, but right now, he was trying to protect his little brother, so Zeus decided that he was going to let this play out.

Still, Sherlock slept on, through one day, then the second.

Zeus knew that John was going to have to leave London soon, and Fates had told him what was going to happen, thought to Zeus it seemed to be the only conclusion.

Zeus knew that his brother would be back... and soon.