Android apps not updating automatically
When an update to an application is published in the Play Store, updates start rolling out. Not all users will see the update immediately; I think the figure is a few hours for the update to be available throughout the country or world. 

The Play Store app checks for updates periodically, I think a few times daily. You can configure toggles to:


Notify when updates are available
Automatically install updates
Notify when automatic updates have occurred 


A user will only be alerted for an update if the application is installed from the Play Store. As a developer, you may have installed from adb, in which case the application will not update from the Play Store. You can always reinstall the Play Store version, which will be updated.