SB 5.21.6

yāvad dakṣiṇāyanam ahāni vardhante yāvad udagayanaṁ rātrayaḥ.
Word for word: 
yāvat — until; dakṣiṇa-ayanam — the sun passes to the southern side; ahāni — the days; vardhante — increase; yāvat — until; udagayanam — the sun passes to the northern side; rātrayaḥ — the nights.
Translation: 
Until the sun travels to the south the days grow longer, and until it travels to the north the nights grow longer.