Using 'today ' in the sentence makes all the difference, 'did not' is used with specific times like within the hour, now, today etc. 'have not' is used in cases where the time period is ambiguous, so the mention of 'today' actually makes using'did not' sensible. – NANDAGOPAL. Mar 5, 2014 at 13:57. Add a comment. More @Wikipedia
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