Little research I have done shows companies will choose beinning of the week, particularly Tuesday morning, to release news if it is going to be positive. Reason being, Monday is kind of a hangover day and not all traders are back to work. Tuesday you can anticipate the majority of traders watching and still gives almost a full week to soak in the news. Wednesday isn't bad, just less time for traders to trade the news. End of the week is usually for news that might not be what was expected... gives the weekend for traders to relax and not impulse sell.
May not be completely accurate, but seems reasonable to me
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