"We don’t know exactly how long it will take," Stone said. "It may take two months, it may take two years."
This is redundant; this is redundant. The writer is saying that you can't predict when Voyager will leave the solar system, and then he (or she) quotes this Stone in saying they don't know how long it will take.
So the first sentence of that quote isn't necessary.
Also, I'd edit the other quoted sentence this way: "It may take two months; it may take two years."
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