“Time immemorial” is usually used poetically today, often in travel shows. So: “men have been fishing in this small Greek village since time immemorial”.
What you might NOT know is that “time immemorial” has an actual start date: June 6, 1189.
The Statute of Westminster of 1275 was the first attempt to codify the laws of England. As part of this, the idea of “time immemorial” was introduced – a time which was declared “the extent of human memory”. The date chosen was Richard I’s accession day. That’s “Richard the Lionheart”, or “Richard Cœur de Lion”, since he spent most of his life in France. The same Richard who left for the Crusades, leaving his brother John to run England… the same King John of Magna Carta and Robin Hood fame.
So the idea was, if there was some kind of land dispute, if a family could find local witnesses to prove that their goats had been grazing on the land since June 5, 1189, then it was generally accepted to be “your land”. You might think of it as a kind of “ultimate statute of limitations”, if you will.