(idiomatic,Britain,Ireland) A very long time ago, from the beginning or as far back as one can remember.
That hat dates from the year dot.
1989, Phil South, Rage Hard (in Your Sinclair magazine, June 1989)
Disk interfaces have been around since the year dot, as people soon realised that the microdrive was unreliable, unstable and generally rubbish for the storage of anything, useless except as a rather small beermat.
References
Year Dot, in LookWAYup Translating Dictionary/Thesaurus.