Earlier quoted context omitted.
Your LG C2 is a dumb tv - if you dont connect it to the internet. You can even buy a $10 IR remote control on amazon and use that to switch inputs. Or, in my experience, all of my external devices support HDMI CEC and auto switch when i use them.
I have an LGCX and if I hadn't connected it to the internet I would have missed out on some important software updates that significantly improved the display performance. I guess you can toggle the internet on and off when updates are published, but it's not the most convenient solution. Edit: But you can use a USB! Woohoo, thank you repliers!
Alternatively, for something more automated, you could just use parental control 'bedtime'. I use it currently to keep the kid from watching TV at certain hours. Could probably do the inverse and block it except for an hour on a particular day, I'd imagine.