If the zuhr time starts at 12:15pm according to the time on Muslim Pro or other apps, when is the zawal time where one should not pray and what’s the duration of zawal?
In actual fact, the word “zawal” literally means the time when the sun moves away from its central meridian and not time it is at its meridian as commonly mistaken. Zawal is the time when Zuhr begins and not the forbidden time (see Radd al-Muhtar). So therefore the usage of the word “zawal” to mean the forbidden time to pray is actually incorrect.
“Istiwa’” on the other hand is the time when the sun is at its highest peak at noon when it is impermissible to perform prayer. People mistakenly refer to this as the time of zawal.
Hence, the time for istiwa’ or the period in which the sun is at its zenith and prayer is forbidden is in reality a very momentary period and cannot be counted in minutes or pinpointed accurately by everyone. Hence, the jurists, out of caution, include a few minutes from either side of it to be the forbidden time for prayer. Therefore, prayer must be avoided for approximately 3-5 minutes before noon and 3-5 minutes after noon, noon being the half way point between sunrise and sunset.
And Allah knows best.
This answer is from a fatwa of Mufti
Abdurrahman ibn Yusuf Mangera.