Answer
(Fatwa: 281/297/N=1434)
Just like Shafai maslak, the Imam Abu Yusuf, Imam Muhammad, , Imam Malik, Imam Ahmad ibn Hambal and as per one saying of Imam Abu Hanifa (رحمهم الله), Asr time starts after mithl awwal. But the famous saying of Imam Abu Hanifa (رحمة الله عليه) is that the time of Asr starts after mithl sani and It is preferred saying as per all the Hanafi Fiqh books and it is stronger as per the proofs. Also in case of offering Asr salah after mithl awwal and before mithl sani, it is doubtful whether the fardh was fulfilled. Hence you should offer Asr salah after mithl sani and should not offer before it. When you reach your shop at 4 o’clock then you should close your shop or adopt any other method and go to mosque for Asr salah when Asr time starts. Do not miss your salah due to shop as well as do not offer it before time (mithl sani).
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband