Tiberius Hemsterhuys (1685-1766) separated this phrase from the preceding entry kappa 933, as it does not occur in the Xenophon passage quoted there. Instead it is quoted from somewhere else: Agathias, Histories 1.5.1 (15.9-10 Keydell); cf. Frendo (13); see on this Theodoridis' Photius edition, vol.II p.LXXV. The king referred to here is Teias, king of the Ostrogoths (cf. PLRE IIIb s.v. Theia), who died in the Battle of Mons Lactarius (modern-day Monte Lettere, in Campania, Italy; Barrington Atlas map 44 grid G4) in late October 552 CE; cf. Bury (270-275).
For the idiom kat' e)kei=no kairou= LSJ (s.v. kairo/s, II.3) cites 'Conon 3', i.e. FGrH 26 F1(III); for other instances see under alpha 249, alpha 2533, delta 273, sigma 490.