I asked Ibn 'Umar: When should I throw pebbles at the jamrah? He replied: When your imam (leader at Hajj) throws pebbles, at that time you should throw them. I repeated the question to him. Thereupon he said: We used to wait for the time when the sun passes the meridian. When the sun declined, we threw the pebbles.
Sunan Abi Dawud Book 11, Hadith 252
← Previous Hadith I saw the Messenger of Allah (ﷺ) throwing pebbles on the day of sacrifice while on his riding beast in the forenoon, and next when the sun had passed the meridian.

Sunan Abi Dawud Book 11, Hadith 251 Next Hadith → The Messenger of Allah (ﷺ) performed the obligatory circumambulation of the Ka'bah at the end of the day of sacrifice after he had offered the noon prayer. He hen returned to Mina and stayed there during the tashriq days and he threw pebbles at the jamrahs when the sun declined. He threw seven pebbles at each of the jamrahs, uttering the takbir (Allah is most great) at the time of the throwing the pebble. He stood at the first and the second jamrah, and prolonged his standing there, making supplications with humilation. He threw pebbles at the third jamrah but did not stand there.

Sunan Abi Dawud Book 11, Hadith 253