Yeah I’m using the fire tv cube, also have Smartthings hub. I haven’t figured out to set up timers (aside from using the tv remote or app)
Id prefer to just say , Alexa, turn off the (room) tv in 30 minutes.
As far as turning off TVs from other devices. Just name your TVs (provided they are connected to some time of hub namely a Fire Tv hub but I’m sure others work as well.)
Again my only desire is the sleep timer, other than that, I’m good.