Why is the expiration of the update token not being returned?

Question

When requesting access / update tokens, the update token is updated, but the refresh_token_expires_in property is not in the API response. I do not know what the official expiration date is. Why is the document property missing?

I get the same response authority for both authorization types of type authorization_code and refresh_token. Below is an example of what I get.

{  
   "token_type": "Bearer",
   "expires_in": "3599",
   "scope": "Calendars.Read Calendars.ReadWrite Files.Read Files.ReadWrite User.Read User.Read.All",
   "expires_on": "1455797016",
   "not_before": "1455793116",
   "resource": "https://graph.microsoft.com/",
   "access_token": "eyJ0eXAiOiJKV1QiL...",
   "refresh_token": "AAABAAAAiL9Kn2Z27Uub..."
}

As you can see, only access token access time is enabled. Bonus question: what is this "not earlier"? I cannot find a link to what this property means.

http://graph.microsoft.io/en-us/docs/authorization/app_authorization , " - , expires_in refresh_token_expires_in, , ".

" " : " ". , , , .

, getHub https://github.com/OfficeDev/microsoft-graph-docs/issues/115