Awwal Waqt means on the start of the time of Salah. We have in the our books what is called Waqt al-Fadheelah for every obligatory prayer which starts immediately on the time of Azaara (Athaan) and goes on till a limit. For Morning prayer Waqt al Fadheela is till the darkness of the sky remains. For Dhohr till two sevenths of the shadow, and Assr till six sevenths of the shadow. For Maghrib prayer it is till the end of red light of the west, and Isha till one third of the night.