Meaning "beyond memory", this type of time originally referred to the period before 1189 A.D.
The first expression comes from English law, where it signifies 
beyond legal... [DOC] [TLE] meaning of time immemorial - All Dictionary [PAR] Oct 1, 2016 ... meaning of time immemorial: the distant last beyond memory; ... Period long ago 
eventually where there is absolutely no recollection or ... year 1275 saying that 
time before King Richard We reign or 1189 ... By a UK statute of the season 1275, 
the year 1189 (first year ... Also referred to as periods of brain.