Get Status / attribute of Sonos sleep timer

I am sorry, but yet not so experienced in Home Assistant.
I have the Sonos Integration installed and working.
I use the service “SONOS.SET_SLEEP_TIMER” (as described here: Sonos - Home Assistant) and the timer is set correctly.

My question is: I cant find an entity or attribute that shows me weather this sleep_timer is set or not to use it for further automation.
I searched in “Developer Tools” → “States” for entity “media_player” and “sonos”, but cant find something showing me, weather a sleep timer is set on a player or not.

Is there a way to get that information somethere?