Laudator Temporis Acti

Greek Anthology 10.43 (tr. W.R. Paton, with his note):

Six hours are most suitable for labour, and the four that follow, when set forth in letters,¹ say to men "Live."

¹ The letters of the alphabet were used as figures: ΖΗΘΙ (meaning "live") is 7,8,9,10.

Ἓξ ὧραι μόχθοις ἱκανώταται· αἱ δὲ μετ' αὐτὰς
    γράμμασι δεικνύμεναι ΖΗΘΙ λέγουσι βροτοῖς.

Thomas More (1478-1535), Utopia, Book II (tr. Robert M. Adams):

Of the twenty-four equal hours into which they divide the day and the night, the Utopians devote only six to work. They work three hours before noon, when they go to lunch. After lunch, they rest for two hours, then go to work for another three hours. Then they have supper, and about eight o'clock (counting the first hour after noon as one) they go to bed, and sleep eight hours.

cum in horas viginti quattuor aequales diem connumerata nocte dividant, sex dumtaxat operi deputant: tres ante meridiem, a quibus prandium ineunt, atque a prandio duas postmeridianas horas cum interquierint, tres deinde rursus labori datas cena claudunt. cum primam horam ab meridie numerent, sub octavam cubitum eunt; horas octo somnus vindicat.

Walter Savage Landor, "William Penn and Lord Peterborough," Imaginary Conversations, Vol. III (London: J.M. Dent & Co., 1909), pp. 9-123 (at 46, Penn speaking):

If all men and women would labor six hours in the twenty-four, some mentally, some corporeally, setting apart one day in the seven, all the work would be completed that is requisite for our innocent and rational desires.