Green’s Dictionary of Slang

1. one who wastes time rather than busying themselves with proper work.

1791		Norfolk Chron. 4 June 2/4: The Fallows, on the fields of early husbandmen, are already well made, while those of Afternoon farmers [...] are so bound by the dry weather, as not to admit of the beccessary pulverisation.
1807		Complete Farmer: General Dict. Husbandy I n.p.: He should constantly be careful to have a sufficient number of hands at work, to make the most of fine seasons; as, without that, he will sustain loss, and have the epithet of afternoon-farmer applied to him.
1825		Massachusetts Agric. Repository 35: It does not require capital to plough a field four and five time instead of twice [...] it is the work, the work, that is wanted, and not the afternoon farmer.
1864, 1867, 1870		Hotten Sl. Dict.
1882		Sydney Sl. Dict. (2 edn) 1: Afternoon Farmer - One who wastes his best opportunity, and drives off the large end of his work to the little end of his time.
1895		C. Crowe Aus. Sl. Dict 3: Afternoon Farmer, one who does not make hay while the sun shines.
1904		Belfast News-Letter 15 June 6: [of a drunkard] One or twoi of the old-time names [...] were expressive. Such as ‘bib-all-night,’ ‘lick-spiggot’ and ‘afternoon farmer’.

2. (US drugs) one who wastes time and neglects work because they habitually smoke opium .

1935

A.J. Pollock Und. Speaks 1/2: Afternoon farmer, an opium smoker who fails to keep appointments. He constantly wastes time and neglects everything, and is dejected, disturbed and morose, unless under the influence of the mysterious poison.