If the 210 days starts on the day he was appointed, the clock runs out on Edward O’Callaghan on 10/30/2018. Don’t know the significance of that other than it’s right before the mid-terms.
Pull quote from the article:
What makes the surprise resignation even more interesting: It was previously thought that she could end up overseeing the investigation into Russia’s meddling in the election and possible collusion with the Donald Trump campaign if Deputy Attorney General Rod Rosenstein had to recuse himself for his role in the firing of FBI Director James Comey (or if Rosenstein were fired).