Asr & Isha Prayer Times

Asr

For the beginning time of Asr, there are two distinct Fiqh positions and both are valid.

Shafi'i, Maliki, and Hanbali fuqaha' agree that Asr time begins when shadow of any vertical object is equal to its length.
Hanafi fuqahaa' say that Asr time begins when the shadow of any vertical object is twice its length.

Both are based on authentic Hadith and practices of Sahaabah

In the Shafi'i school, 'isha time enters at the disappearance of the red twilight.
Most prayer timetables, calculate the time for 'isha according to the disappearance of the white twilight.
The exact time when the red twilight disappears varies from place to place.
It could be more than 45 minutes, or it could be less than 45 minutes. Some say it is about 2 / 3 of the time between Maghrib & Isha shown on most timetables.
The position of Abu Yusuf and Muhammad ibn al-Hasan (Abu Hanifa main students), and Imams al-Shafi`i, Malik, and Ahmad, is that isha time comes in when the redness in the sky disappears.
Imam Abu Hanifa considered Isha to have begun with the disappearance of the white twilight which occurs long after the disappearance of the red from the horizon and with the onset of complete darkness. This is the relied upon position in the Hanafi school