Here's a math problem: if Train A leaves the station at 60mph, and Train B leaves the station at 30mph, when are they going to receive Windows 10 Insider Preview Build 19033? The answer was "yesterday," when Microsoft decided to release the latest preview build to both Fast and Slow ring members of the Windows Insider Program.
Preview Build 19033 is unremarkable on its own. Microsoft said in its blog post that it fixed some bugs, heard about some known issues and collected information about the 2019 American Music Awards to convince people to sign up for the Bing Insiders Program.
The bigger change has yet to come. Microsoft explained in the announcement:
NOTE: We are looking to begin releasing new builds from our development branch. This means we will be releasing builds to Insiders in the Fast ring from the RS_PRERELEASE development branch again instead of the VB_RELEASE branch. This also means the desktop watermark will be returning with these builds. As is normal with pre-release builds, these builds may contain bugs and be less stable. Now is the time to check your Windows Insider Settings and switch to the Slow ring before if you wish to remain on 20H1.
The company also said that Fast ring members of the Windows Insider Program who "have selected to stop getting Insider Preview builds when the next major release of Windows 10 is available" will be moved to the Slow ring "until 20H1 is finalized." Insiders were encouraged to check their settings to make sure they're correct.
More info about the latest preview builds is available via Flight Hub. (Although the most recent entry is Preview Build 19030, which debuted on November 22, so it's not clear how long it will take Microsoft to add Preview Build 19033.) Further details can be found via the Windows Insider Program documentation on Microsoft's site, too.