You should perform the nafilah from when the sun passes the...
Then he prayed two rak’ahs after Dhuhr and before the time of ‘Asr he prayed (another) two rak’ahs, and when the shadow reached two cubits he prayed the ‘Asr prayer. When the sun had set, he prayed the Maghrib prayer, and the time for the ‘Isha prayer entered when the twilight had passed. The end of the time for the Maghrib prayer is at nightfall. Then the time of ‘Isha enters and it continues up to a third of the night. After the ‘Isha prayer, he (S) would not pray until midnight.
Similarly, al-’Ayyashi has mentioned other narrations on the time for the nafilah of Dhuhr as has al-Saduq and others.[^12] It should be noted that all the rak’ahs of the nafilah of ‘Asr were not mentioned in this narration. Apparently the statement ‘ ...and before the time of ‘Asr he prayed ...’ is just explanatory of what precedes it.
In al-Tahdhib: In his narration from Muhammad ibn ‘Ali ibn Mahbub from ‘Abbas ibn Ma’ruf from ‘Abdillah ibn Mughirah from Mu’awiyah ibn Wahab who said: I heard Aba ‘Abdillah (as) saying – as he recollected the prayer of the Holy Prophet (S): He would bring his ablution water, cover it and place it near himself, and he would put his siwak under his bed then he would sleep for as long as Allah willed.