Green’s Dictionary of Slang

a day; thus phr. one of these odd-come shortlys, one of these days, sooner or later.

1738		Swift Polite Conversation 7: col.. Miss, when will you be married? miss. One of these odd-come-shortly’s, Colonel.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Odd come shortly I’ll do it one of these odd-come-shortly’s; I will do it some time or another.
1788		Grose Classical Dict. of the Vulgar Tongue (2nd edn) (3rd edn).
1815		(con. 18C) W. Scott Guy Mannering (1999) 149: She’ll sing out one of these odd-come-shortlies.
1824		W. Scott St Ronan’s Well (1833) 191: They say she is to be married and off to England ane of thae odd-come-shortlies.