Android Question StartServiceAtExact doesn't start at the exact time.

How do you see that the service is delayed? Are you monitoring the logs?

Try to acquire a wake lock immediately when the service is started (and release it when it is no longer needed).

Another thing you can do is to wake the phone a few minutes earlier and use a standard timer together with a foreground service and a wake lock to make sure that it "rings" at the exact time.