The markets open on Sunday evening at 5:00pm (Chicago Time) - Many buy & sell orders have been placed with brokers over the weekend (while the market is closed), and are actually executed within the first few minutes of the market's open.
The difference in the timing of each brokerage's orders, and the sporadic reporting of initial large transacions, can cause wild swings in the first hour of trading, as the system takes a bit of time to equalize. and adjust to the push and pull of the "accordian effect" that always follows the release of pent-up stress of the preceding two days of suppressed trading pressure.
The initial first two hours of wild swings can be disregarded as "radio noise", and we can then focus on actual world-market response, until next Friday night.
