this has happened to me in the past. Yes, you need to go into the settings menu and it will tell you the time before the tv switches itself off. You will be able to advance that time easily.
It's nothing to do with your Sky Q box. The message is generated by your telly, so you need to press any button on the ***TVs*** remote control (and NOT the Sky Q one) to prevent the set switching itself off.
There is a simple option - just change the volume occasionally - that way the tv will register that its still being viewed and not think its been left unattended.