From Online Etymology Dictionary:
early 14c., “narrative dealing with a happening or an event,” from Old French legende (12c., Modern French légende) and directly from Medieval Latin legenda “legend, story,” especially lives of saints, which were formerly read at matins and in refectories of religious houses, literally “(things) to be read,” on certain days in church, etc., from Latin legendus, neuter plural gerundive of legere “to read; to gather, pluck, select,” from PIE root *leg- (1) “to collect, gather,” with derivatives meaning “to speak (to ‘pick out words’).”
Extended sense of “nonhistorical or mythical story,” with or without saints, wonders, and miracles is first recorded late 14c. Meaning “writing or inscription” (especially on a coin or medal) is from 1610s; on a map, illustration, etc., from 1903. To be a legend in (one’s) own time is from 1958.”
Pascal Tréguer writes at wordhistories.net:
“…In this case too, the Oxford English Dictionary (3rd edition, 2016) erroneously says that a legend in one’s (own) lunchtime was first used by Christopher Wordsworth in Death at the wicket, the review of Testkill, a cricket murder mystery novel by the English cricketer Ted Dexter (born 1935) and the English sports writer Clifford Makins (1924-90)—review published in The Observer (London) of Sunday 20th June 1976:
Cricket, we have been told often enough, is not so much a game as a Way of Life and there are many books devoted to the theme. Cricket as a Way of Death, the cricket-and-crime nexus, has been less celebrated […].
Now along comes Testkill to repair some of the leeway, as topical as inflation but a great deal more interesting, the exotic fruit of collaboration between a batsman who will rank up there with R. E. Foster and the hard-hitting immortals and a former sports editor of The Observer who was a legend in his own lunchtime.
“The Dynamic Death-Defying Leap of Timothy Satupon the Great,” at the Library Theatre, Scarborough, is a play about the sort of fantasies people imagine that those who work in offices indulge in.
Peter Hawkins, whose first play this is and who is on the staff of Radio Durham, used to be a clerk himself, so maybe this is an attempt to exorcise the demons that lurk in the ledgers of his mind. If this is so then his own rite is very agreeably conducted.
“Timothy Satupon” owes a bit to “Billy Liar” and quite a bit to what went before and what has followed it. Timothy himself is a nice young lad, a legend in his own lunchtimein the sub-Dickensian office of Baron, Bound and Bondage of Fetter Lane (where else), where he eyes up the dollies, but never quite makes it, and is never quite seduced either by the comic gorgon of a boss who wants to keep him indentured and indebted to the family business.
The second-earliest instance of a legend in one’s (own) lunchtime that I have found is from the column Lighter Side of Washington, by Don Mclean, in the Springfield Daily News(Springfield, Missouri) of Wednesday 14th February 1973:
Funny remark about a senator who disappears from his office every day about noon to 3:30 or 4 p.m., usually returning somewhat tipsy:
“He’s a legend in his own lunchtime.”.”