The best known economic releases, inflation and jobs among them, are published at 8:30am Eastern. The stock market is shut at that hour, so the first reaction happens in futures. A second group of releases comes out at 10am, half an hour into the cash session. The timing changes how the reaction looks.
What comes out at 10am
The purchasing manager surveys covered in ISM and PMI are published at that hour. So is the monthly report on job openings, and so are the main consumer sentiment readings. Several housing figures share the slot.
These are mostly second-tier releases. They move the index less often than inflation or jobs data. When the market is focused on growth or on the labor market, one of them can carry a whole session.
No gap, a spike
A pre-market release shows up on a stock chart as a gap at the open. The index ETF never trades the prices in between. A release during the session has no gap to hide in. The move prints tick by tick, in full view, with every option quote repricing as it goes.
That makes the reaction look sharper than it is. A move of the same size before the bell would be one step on the chart. Inside the session it is a fast candle with volume attached.
It lands inside the opening range
The first half hour of trading sets a high and a low that many intraday traders use as reference. A release at 10am arrives just as that range is being completed. It can break the range within a minute, or reverse a move that had looked settled.
This is one source of the reversals described in the first-hour reversal. A range drawn on a day with a release in the middle of it deserves less trust until the number is out.
Dealer hedging is live
Before the bell, option dealers cannot adjust hedges in the ETF itself. At 10am they can and do. A release that pushes the index toward a level with heavy positioning meets hedging flow straight away. Whether that flow dampens the move or adds to it depends on which side of the gamma flip price sits.
Same-day options are already open
An option expiring that day has been trading for half an hour when the release hits. It carries a little event value until the number is out, then loses it within minutes. A trader who bought at the open is holding that event whether they meant to or not.
Where NoVo shows it
The Trader dashboard shows net GEX, the gamma flip, the call and put walls and the expected move on SPY, QQQ and IWM during the session, on a five-minute cycle for Trader Pro and live for Trader Max. Dr. NoVo, a markets SI, writes the read on where price sits once the release has passed.