Green’s Dictionary of Slang

wait a moment, hang on.

1900		Marvel 22 May 15: Half a mo’, an’ I’m after it!
1910		H.G. Wells Hist. of Mr Polly (1946) 197: ’Arf a mo’, mister.
1921		D.L. Sayers Unpleasantness at the Bellona Club (1977) 29: Half a mo’ while I deposit my outer husk.
1922		Joyce Ulysses 82: - Ascot. Goldcup. Wait, Bantam Lyons muttered. Half a mo.
1937		J. Curtis There Ain’t No Justice 46: ‘Going home, Tom?’ said Fred. ‘Yes.’ ‘Half a mo’. I’ll come with you.’.
1943		R. Llewellyn None But the Lonely Heart 58: ‘Half a mo,’ she says. ‘Where you going?’.
1950		A. Buckeridge Jennings Goes To School 102: ’Ere, ’arf a mo.
1959		D. Niland Big Smoke 116: ‘Half a mo, Father,’ Pretty Joey said. ‘Show us that again for a minute.’.
2003		(con. 1934) W. Woodruff Beyond Nab End 77: Pa Hargreaves calling, ‘’Arf a mo. ’Arf a mo,’ and the dog barking, and Ma Hargreaves yelling.