I have an iMac with a Fusion drive running High Sierra. Time Machine is enabled and backs up to an external disc.
Time Machine takes daily local snapshots so that you can go back to a specific day, even if you don't plug in your backup disc every day.
Unfortunately, this feature is enabled only on laptops, as the aforelinked page says.
How do I tell Time Machine to enable it on my iMac? I plug in my external disc only once a fortnight to backup, but I'd still like to go back to a particular day's snapshot, say if I overwrote a file.