I asked Ibn ʿUmar, "When should I do the Rami of the Jimar?" He replied, "When your leader does that." I asked him again the same question. He replied, "We used to wait till the sun declined and then we would do the Rami (i.e. on the 11th and 12th of Dhul-Hijja)."
إِذَا رَمَى إِمَامُكَ فَارْمِهْ فَأَعَدْتُ عَلَيْهِ الْمَسْأَلَةَ قَالَ كُنَّا نَتَحَيَّنُ فَإِذَا زَالَتِ الشَّمْسُ رَمَيْنَا
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.
إِذَا رَمَى إِمَامُكَ فَارْمِ فَأَعَدْتُ عَلَيْهِ الْمَسْأَلَةَ فَقَالَ كُنَّا نَتَحَيَّنُ زَوَالَ الشَّمْسِ فَإِذَا زَالَتِ الشَّمْسُ رَمَيْنَا