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System Preferences > Energy Saver.
It hasn’t changed in decades. It’s still there in High Sierra.
I suppose it could also be
System Preferences > Desktop & Screen Saver > Screen Saver > Start after: [ XX Minutes ].
Updated: Your new screenshot shows that System Preferences is opening to show the iCloud pref pane only. You need to click the button that looks like a grid of dots to get back to the main view where you can select pref panes from a grid of icons.
I've tried that, but I don't get those option. Please see the edit to my question. I've added a screenshot of what I get when I click System Preferences. – Martin Muldoon – 2018-03-16T15:00:22.520
@MartinMuldoon I’ve updated my Answer to help you get back to the main screen of System Preferences. – Spiff – 2018-03-16T15:04:07.293
@MartinMuldoon Glad I could help. Honestly it’s weird that it got stuck on one pref pane quitting the app and re-launching it should have returned you to the main icon grid view as well. ♂️ – Spiff – 2018-03-16T15:07:22.220
What's even stranger based on what you just said, is that I have to Macbooks and both had the issue. Cheers! – Martin Muldoon – 2018-03-16T15:19:57.877