Market-moving overnight news doesn’t happen that often.
It's not just market-moving news - it's also moves in other markets that can make the closing price stale. If you recall a few years ago, there was a scandal with some mutual funds that had extensive foreign holdings that allowed a select few holders to freely trade in and out of the fund. These holders were allowed to trade based on stale closes (in other words based on the foreign close) when other markets had made moves since that close. It was basically a license to print money at the expense of other holders of the fund.
So it just seems to me that the risk for the MM is higher when the home market is closed, and higher risk for the MM should correspond to a worse price for you.
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