Green’s Dictionary of Slang

the first opportunity.

[1542		Udall (trans.) Erasmus’ Apophthegms (1564) Bk II 293: Doe ye not here euen at the first chop se and knowe of old, the nature and facions of Alexander the great].
1915		Kipling ‘Sea Constables’ in Debits and Credits (1926) 30: Didn’t care what he hugged, so long as I could lie behind him and give him first chop at any mines that were going.