The angle chosen is the primary Hanafi opinion of 17/18 degrees correlating with shafaq al-abyad. However, during daylight saving time (BST), shafaq al-ahmar is adopted due to late Isha in the UK and higher latitude nations. During persisting twlight where the Maghrib twilight lasts until Isha, 11:15pm will be the adopted time as per aqrabul ayyam.
12/17°- The onset of shafaq al-ahmar via observational data in higher latitude countries (12°during BST/Summer).
15°- The onset of shafaq al-abyad via observational data and the onset of shafaq al-ahmar via historic angular calculation.
18°- The onset of shafaq al-abyad via historic angular calculation.
The times of Isha fall into the early shafaq al-ahmar - the Red Twilight - and the later shafaq al-abyad - the White Twilight. The majority of classical scholars consider the early time as the commencement of Isha while others hold the later opinion. However, in high latitude countries - 48°and above - observational data shows that 12°and 15°correlates with early and late Isha as opposed to the classical association for both being at 15°and 18°respectively.