How to get an FCM token unambiguously? In what cases is it not available? In what cases is it reissued?

Question

Android

I don't know if I should ask all three questions in 1 "topic", but I'll try.
1) How to get an FCM token unambiguously?
In the current application, obtaining an FCM token is a prerequisite for its operation, so at the very beginning I try to get it using the command (this, by the way, is also a minus of this solution, is there a replacement for FCM if it is missing?)

String fcmToken = FirebaseInstanceId.getInstance().getToken();

First but. It takes some time to generate it (as they say in foreign sources - "usually less than 10 seconds, depending on the Internet, device load, etc."). Thus, I will have to start a thread that will check the presence of a token every N seconds, and if it is received, then continue the application, which seems to me ... well, wrong, although I don’t see any other way.
2) In what cases is it impossible to obtain it?
Second but. To create it, there are several conditions known to me - the presence of google-play-services on the device, as well as an Internet connection. Is this the final list or are there any other dependencies/conditions?
3) In what cases is it issued again?
The function responsible for getting a token in the service is called

@Override
public void onTokenRefresh() {}

The name of the function, to put it mildly, hints at the fact that a new FCM can be issued (and why even a whole service to get a token, FirebaseInstanceIdService ). In what cases can this happen? Perhaps the name of the function is misleading me?