How often to Home Screen widgets update
Apple designed Home Screen widgets to be efficient to ensure your iPhone performance and battery life is maintained. With that Home Screen widgets do not refresh all the time and update at certain periods during the day. Developers set a schedule as to how often a widget should refresh its data but it's ultimately up to your phone when it wants to do this. In Apple's support documentation it details that your iPhone learns from your behaviour and prioritises the apps you use most. See here: https://developer.apple.com/documentation/widgetkit/keeping-a-widget-up-to-date
All of ETA's widgets are refreshed when you open the app. We also request that the data should be refreshed every 15 minutes. In the real world, if you use the ETA app frequently, you should expect a widget to update at least 2-3 times an hour. If you don't use the app much at all then you might only see the widgets update a few times a day. Our live tracking update shows a time of when the widget was last updated.
The Home Screen widgets are definitely supposed to update on their own but we have no control over the frequency. In my own personal testing I've seen it go out to 4-5 hours, and sometimes it's a short as 15 minutes. These are a bit of a black box as we tell iOS when to update but it's ultimately up to your phone as to when it will. In our latest release we added more updating options including refreshing the widgets when you launch the app. We do see that the more you use the ETA app itself the more your iPhone prioritises Home Screen widget updates.