yāvad dakṣiṇāyanam ahāni vardhante yāvad udagayanaṁ rātrayaḥ.

yavat-until; daksina-ayanam-the sun passes to the southern side; ahani-the days; vardhante-increase; yavat-until; udagayanam-the sun passes to the northern side; ratrayah-the nights.