Green’s Dictionary of Slang

the hanging day.

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Wry Neck Day. Hanging Day.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1862		E. de la Bédollière Londres et les Anglais 319/1: wry neck day, [...] jour d’exécution.