Click and hold on the Time Machine icon in the doc - select "Back Up Now" and your done🙂
To resume backing up, press the Control key while you click the Time Machine icon in the Dock, and then choose Back Up Now from the menu."
It would also use to much power to have it on overnight.
How much does the UK charge for electricity? I have never turned a computer off over night since my first hard drive based computer, which was a Commodore Amiga 500 with a 750MB Hard drive.