How can we calculate the times

Q 1: When Allah made these five Salah (prayers) obligatory for the Messenger of Allah (peace be upon him), which was the first time when Salah was offered? On what day did the Qur'an start to be revealed to the Messenger of Allah (peace be upon him)?

A: They began with the Zhuhr (Noon) Prayer, as the Messenger of Allah (peace be upon him) performed it, led by Jibril (Gabriel, peace be upon them), at the beginning of its time. As for the Qur'an, it was first revealed to the Prophet (peace be upon him) during the month of Ramadan. Allah, the Exalted, says, The month of Ramadan in which was revealed the Qur’ân, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). (Part No. 6; Page No. 124) However, we do not know of any proof that specifies the exact day it was first revealed.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.