 Why does it take the aliens so long to make a decision about what to do?
But this vast distance did not mean that isolation could endure forever. Instruments within the ship intercepted radio broadcasts and, within the hour, early TV signals. The history of the planet was tabulated as facts became available. A meteor shower could pass over and their clumsy instruments could interpret it as an all-out enemy attack." "In a week we can't negate their entire history. "And how long can Earth last? They went much closer to Earth, not intending to commit themselves. For a day they circled the planet, avoiding radar detection, which for them was not difficult, testing, and sampling.
 They cannot decide if they have time to make a difference before they have to be somewhere else.
 They do not know if it is worth the time to learn a human language to try to convince the humans to maintain peace.  They are cautious because they do not want to get hit by a missile or bomb.  The aliens do not actually want to help, but are required to, so they are hesitant to make a move.  They cannot decide if they have time to make a difference before they have to be somewhere else.