What is the meaning of "Dahw Al-Ardh"? and when it happened?

In the Islamic calendar, the 25th of Dhu Al-Qi'dah is the day of "Dahw Al-Ardh", one of the greatest scenes of the creation, a solemn incident in the exquisite divine creation. The Almighty Allah in (79:30) speaking clearly about Dahw Al-Ardh says: {And the earth, He expanded it after that (Dahahaa)} and {And [by] the earth and He who spread it} (91:6) .
It is the day when the earth was spread for the advantage of human beings. The phrase "Dahw Al-Ardh" literally means "The spread of the earth". On this day Allah (swt) spread out ALL the land on the Earth from under the Ka`bah.
In another tradition it is reported that the first Rahmah & blessing descended on this very day.... It is also reported on the authority of Imam Ali bin Musa Ar-Redha (peace be upon him) that tonight the two distinguished Prophets ie Prophet Ibrahim (peace be upon him) and Prophet Issa (peace be upon him) were born. Therefore it is a highly blessed night & day to be spent in prayer and supplications. If a person fasts on this day, it would act as a Kaffarah (Penitence) for his sins of seventy (70) years. And according to a Hadith from the Prophet (blessings of Allah be upon him and his family), whoever fasts on this day (25th of Dhul Qa’dah), everything that is between the heavens and the Earth will ask repentance for him from Allah (Glory and Greatness be to Him).
The first place identified on earth was the position of Ka'bah, then Allah has expanded the land around it as it is the center that earth was spread around it, which was stated on narrations of Ahl Al-Bayt (peace be upon him), who have also stated that it was two thousand years after the creation of earth.
Which means that earth was created long time before its spreading on the 25th of Dhu Al-Qi'dah, like it is stated in this narration of Imam As-Sadeq (peace be upon him): "The Almighty God has spread the earth from under the Ka'bah to Mina, then from Mina to 'Arafat to Mina, So the earth is from 'Arafat, and 'Arafat is from Mina and Mina is from the Ka'bah." (Tafseer Noor Thaqalayn ch.5, p:502).
Being distinctively honorable, at this night the mercy of Almighty Allah is poured on people. A great reward is obtained by those who practice acts of worship at this night. Ali ibn al-Hasan al-Washsha’ has narrated that when he was young, he was with his father in the hospitality of Imam Ar-Redha (peace be upon him) at the twenty-fifth night of Dhu’l-Qa`dah. After they had their supper, Imam Ar-Redha (peace be upon him) said, “At the twenty-fifth night of Dhu Al-Qi'dah, Prophet Ibrahim was born, Prophet Jesus the son of Mary was born, and the earth was spread on the water where the Holy Ka`bah is now situated. Hence, if one observes fasting on this day, he will be given the reward of observing fasting in sixth months.” According to another narration, Imam Ar-Redha (peace be upon him) added, ﴾Verily, on this day, al-Qa'im (i.e. Imam al-Mahdi) will appear.
According to Mafatih Al-Jinan of Sheikh Abbas Al-Qummi: Apart from fasting, worship and ghusl, there is a special prayers as follow: Pray a 2 units prayer at the time After sunrise and before breakfast time. In every unit, after the recitation of Surah Al Fatihah once, recite Surah 91-Ash Shams- five (5) times. After the Salaam recite the following: "There is no power and no strength except Allah's the Highest High, the Al-mighty. O He who tolerates lapses, bear with my false steps, O He who responds to supplications, answer to my prayers. O He who pays attention to (all) voices, hear my cry, and have mercy on me, overlook my wrongdoings and opposition, O Owner of might and majesty."