You were on the nearer side of the valley, and they were on the farther side, and the caravan was below you. Had you wished to set a time by mutual agreement, you would certainly have disagreed on the timing. However, the encounter took place, so that God might settle a matter which had already been ordained, so that he who was to perish might perish after clear evidence of the truth, and he who was to live might live in clear evidence of the truth. Surely, God is all hearing and all-knowing.