The sunset and with Allah's success: It is not valid to perform it before this time; because it has become obligatory in full, and cannot be fulfilled with a deficient performance; as reported by Uqbah ibn Amir al-Juhani, may Allah be pleased with him, who said: "There are three times when the Messenger of Allah, peace be upon him, forbade us to pray or to bury our dead: when the sun rises until it is fully risen, when the sun is at its zenith until it tilts, and when the sun begins to set until it sets," in Sahih Muslim 1: 568, Musnad al-Mustakhraj 2: 424, Sahih Ibn Hibban 3: 348, Sunan al-Tirmidhi 3: 348, and Sunan Abu Dawood 3: 208. And from Ibn Abbas, may Allah be pleased with both of them, who said: "Witnesses who are trustworthy and the most trustworthy among them to me is Umar, that the Prophet, peace be upon him, forbade praying after dawn until the sun rises and after Asr until the sun sets," in Sahih al-Bukhari 1: 211. As for if it is performed at this time, it is permissible to perform it without dislike, but it is preferable to delay it; to perform it at the preferred time; because it does not become missed by delaying, unlike the Asr prayer. Refer to: Al-Wiqayah p. 137, and Tabyeen al-Haqaiq 1: 85, and Allah knows best.