I think after Google approves of the build, it then goes to the Android phone and tablet manufacturers, who then do one final check, because they're the ones that say which of their phones and tablets can run the app. Each phone manufacturer might have a different approval processing speed.
While I can't rule this out completely, this scenario is highly unlikely. First, for each Android version each manufacturer has to certify its devices against Google specs. If a device comes out with some Android version or later on has an update option to a more recent Android version, it should be able to run every app compiled for this version. With the only exception that some devices don't have specific optional components (like NFC for example) and therefore won't be able to run apps that require those components. And second, just imagine how many employees each and every phone manufacturer would need to test each version of every app against all the models that this company sells or has sold. That would be thousands, if not millions, given the number of updates that get pushed to the Play Store each day. And smaller manufacturers wouldn't be able to even do this at all. Usually, incompatibilities of some app with some specific phone model are addressed (by the app developer) when an affected user reports this by filing a bug report to the app's bug tracker. The manufacturer won't even bother with this unless it's an app that 90% of all users have installed (if apps of the size like Instagram won't run on all devices of a specific brand, then the manufacturer will surely investigate this). It might be sad to hear for all of us WZ players, but Samsung and the other brands couldn't care less about niche apps like WZ.
