Are the four rak'ahs mentioned in the Hadith referring to Duha prayer, and what is the time of zawal (declination of the sun)?

The time of zawal (sun's declination) is when the sun moves from the middle of the sky towards the west (Maghrib), and it signifies the beginning of Dhuhr prayer time. As for the four rak'ahs mentioned in the hadith, they are not the Duha (forenoon) prayer. Instead, they are either the sunnah prayer before Dhuhr, or an independent prayer that the Prophet, peace and blessings be upon him, used to perform after zawal, as the gates of heaven are opened at this hour.