When does the time of ‘asr prayer start and end?
As the beginning of ‘asr time depends on the end of dhuhr time, the dissensus about the end of dhuhr time affected the start of ‘asr time too. Therefore, according to Imam Abu Yusuf, Imam Muhammad and imams of other jurisprudential schools, dhuhr time ends and ‘asr time starts when the shadow of everything gets one time longer than itself, except “fay al-zawal”. This is called “ asr al-awwal” (the first time of ‘asr prayer). According to Imam Abu Hanifa, the time of dhuhr prayer ends and ‘asr starts when the shadow of something gets two times longer than itself, except “fay al-zawal”. This is called “asr al-thani” (the second time of ‘asr prayer). Presidency of Religious Affairs takes as basis the practice of asr al-awwal in its calendars.
The last time of ‘asr prayer is the time just before sunset. However, one should not postpone it until this time without a valid excuse. The Prophet Muhammad (saw) described establishing asr prayer negligently by postponing it until sun gets yellow as the prayer of hypocrites (See. Abu Dawud, Salat, 5). But if one could not establish it earlier, s/he may establish it even the sun is about to set (Kasani, Bada’i, I, 124; Marghinani, al-Hidayah, I, 256, 261-262; Zaylai, Tabyin, I, 80; Ibn Qudamah, al-Mughni, II, 15-16). Indeed, the Prophet (saw) said, “Whoever could get one rakat of ‘asr prayer before sunset, he has got the ‘asr prayer.” (Bukhari, Mawaqit, 28)
According to the Shafi›i school, the time of ‘asr prayer is divided into five in itself: “virtuous”, “optional”, “permissible without makruh time”, “permissible with makruh time”, and “excuse”. Excuse time is the establishment of ‘asr and dhuhr prayers within dhuhr’s time by combining them due to journey or rain. As for the other classifications, virtuous time is the time until the shadow of everything becomes one and a half times longer than itself; optional time is the time when the shadow of an object becomes two times longer than itself; permissible without makruh time starts with the optional time until the sun gets yellow; and permissible with makruh time starts when the sun gets yellow until it sets. It is not permissible to postpone ‘asr prayer until the time of permissible with makruh time unless there is an excuse. However, one who establishes even one rakat of ‘asr prayer before sunset is deemed to have established it in time (Nawawi, al-Majmu’, III, 27).
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS