More of a question...

[KennyGoers]

Is being exported really a requirement? I have a running service is O and didn't set the exported flag and it appears to be running fine, is it situational?

[MinceMan]

I'm guessing this question is about JobScheduler. It's all about how your service is started which determines if you have to export (make it visible to the rest of the device/system) or not. A JobService is started by the system so I'm pretty sure that you have to export it. If you have a service that you start within the app then you do not have to export it.

The O background limitations are another beast. You can start a background service if your app is in the foreground and for up to 30 seconds (do not expect this time) after your app has been backgrounded. After that your services will be shutdown. If your app is not in the foreground you more or less have to make your service a foreground service with a notification. Registering with the Job scheduler is the supported way around this problem but not for long running operation (do not use it to display music controls). Unless you are literal an alarm/timer/clock app you should not use AlarmManager as it is deprecated by the system for any other purposes.