To one who asked what was the proper time for lunch, he said, "If a rich man, when you will; if a poor man, when you can."This is fragment 183 of Diogenes the Cynic in Gabriele Giannantoni, ed., Socraticorum Reliquiae, Vol. II (Naples: Bibliopolis, 1983), p. 493.
πρὸς τὸν πυθόμενον ποίᾳ ὥρᾳ δεῖ ἀριστᾶν, "εἰ μὲν πλούσιος," εἶπεν, "ὅταν θέλῃ· εἰ δὲ πένης, ὅταν ἔχῃ."
Also attributed to Bion, in slightly different form — see Jan Fredrik Kindstrand, Bion of Borysthenes: A Collection of the Fragments with Introduction and Commentary (Stockholm: Almqvist & Wiksell, 1976 = Studia Graeca Upsaliensia, 11), pp. 130, 296-297 (F80).