Just posting an update from the manual.

I've found that you can turn on Timeshift by going to "Info" while watching a channel and then pressing and holding down the button in the middle of the arrows (the "Enter" button).
This brings you to a screen where you can choose to Record the program or turn on Timeshift.

BUT WHY??? I still can't work out how to just turn it on permanently. When I do the above it is on until I turn-off the TV. So why not just allow me turn it on by default every time I turn on the TV? Or is there a way????? Thanks.