This article relates details not found by me elsewhere.
The man was slain when he made his usual trip out on to his balcony where he was alone. That is the two missiles, said to have lots of blades, killed him with no collateral damage to others, especially family. The specific missile is alluded to because there was no explosion, no noise. It apparently kills cleanly.
So the interval of 6 months was required to organize the slaying and then wait for the precise circumstances required for success.
This is my interpretation of various accounts I have read.
My question is, where did the drone come from?
From anywhere. The long range drones have a range of ~15K miles. If they have to fly at lower altitudes, obviously the range is less.