Short story? Received by IOC's Whitehorse attorney by February 21.
I spoke with one of Phil's attorneys, John Christian, on this very question. A notice to rescind one's dissent must be received by IOC's attorney in Whitehorse just before the deal actually "closes" i.e., 1-2 days after the Yukon court approves the deal. Per the MIC, IOC's post vote court date is Mon. Feb. 20. Normally, a deal can be approved by the court the same day. Then, 1-2 days to complete the filing and transfer type stuff. However, "normally" might not occur in this case. Phil may well be there with some kind of case to be made. Even if Phil were not there, considering the history of this deal, the Supreme Court might want to take a few days to review this deal anyway
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So, Feb. 21 is the earliest possible deadline.