not sure if this is the date you are looking to find but it would seem logical to think the time to file might be based on the "completion date" of the spinoff which was april 24.
“2015 has already seen significant progress, highlighted by the successful completion of the spinoff of Communications, Sales and Leasing (‘CS&L’) on April 24,” said Tony Thomas, president and chief executive officer. “This transaction has made Windstream a stronger company with less debt and increased capacity to invest in our network and create value for our shareholders.”
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