Bottom line: Pre-ordering a Pixel 3 or Pixel 3 XL from Google will no longer get it to you on day one. It is probably worth waiting for a promotion if you are interested in buying one since pre-ordering will not get you a phone much faster anyways.
Even though Google has just opened up pre-orders to the Pixel 3 and Pixel 3 XL yesterday, those hoping to get one soon may be faced with slightly delayed shipments. October 18 is the first day that consumers can get their hands on a device, but according to Google's own store page at checkout, those who did not already order will have to wait an extra few days.
Even when paying up for expedited shipping, the absolute earliest delivery from the Google Store is now only guaranteed by Tuesday, October 23. It does not appear to matter what color is selected nor whether the phone is purchased as unlocked, for Verizon, or Project Fi.
Considering the $150 increase given the Pixel 3 over the Pixel 2, it raises the question of whether Google is again facing supply and logistics issues getting their latest devices out on time or if that many people just decided to bite the bullet and pay up. Considering that Google is not offering any promotions to US customers for the time being and the lack of major hardware changes, the former seems more likely.
Provided you can look past the giant notch and are willing to part ways with nearly $1,000 after taxes, the larger variant may ship out a day later on the 19th. Depending on your location, the Pixel 3 XL is still expected to arrive at similar times to the Pixel 3 just one day later.
One thing to note is that buying from Verizon and picking up a device in store should be possible on October 18, but may result in receiving a device with a locked bootloader as well as unwanted Verizon apps pre-loaded onto the phone. If you do not know what that is, it probably will not matter to you. For tinkerers and hobbyists interested in loading custom ROMs, buying unlocked is by far the safer option even if it means waiting a little longer.