2010 to 2018 according to the opener.
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Yes, as the intention was stated before either sheet was posted, the timer should start from the time MB posted with no additional buffer as both players were aware they were in competition.
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Based on the wording of the rules, that 24hr window is only applicable from the time the intent is stated therefore stating it within the 48hr window does not add any additional buffer.
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Write what you know I guess