Sam, 2 things. 1 - SLV is a very liquid ETF and had 309,137 shares trade at the opening auction today. You are not going to have an issue with this ETF. 2 - The issue will come into play for illiquid ETFs with little or no opening auction volume. The greater the percentage of volume your order for the opening auction is, the greater the influence it will have on the opening price. PALL only traded 1,976 shares at the auction at a price of 210.81, which was above the ask price of 209.87 at the time. There is no reason not to always use a limit order. It won't affect the price you order trades at but will prevent you from getting a fill at a price you don't want.
I've had delayed confirmations with IB where the trade notification time does not match up with the auction time in the time and sales. Either way, I really just wanted to point out that you are not going to always get a fill notification at 09:30 or 16:00, regardless of reason.
Just look at Sam's timestamp for today. It shows a trade time of 09:30:12. My time and sales shows the auction went through at 09:30:00.
If you mean SAM then the auction did happened at 09:30:00 (369.50). If you had an execution at 09:30:12 then that was the FINRA executed trade at 371.79 but that's obviously not part of the auction.
In my experience, NYSE auction are usually delayed and auction price times&sales corresponds with the exact moment IB notifies in trade log.