Green’s Dictionary of Slang

eight-day clock n.

(Aus.) the penis.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 9: It seemed like no time at all that her Onkarparingas had slipped a Dunlop overcoat on his eight-day-clock and the contract had been fulfilled.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 39: The signal was coming right from my eight-day. You know, eight-day clock.
2005		M.B. ‘Chopper’ Read Chopper 4 89: The Japanese navy sailors were noted for being a bit small in the eight-day-clock department.