Extreme latitude methods

[mohamed]

I have a question about extreme latitude methods implementation in praytime. What is the criteria for setting Fajr/Isha time to "invalid"?

[orasul]

I have a question about extreme latitude methods implementation in praytime. What is the criteria for setting Fajr/Isha time to "invalid"?

According to https://en.wikipedia.org/wiki/Twilight. Night starts and ends at the moments when Sun is under horizont line at some angle. 18, 16, 20 etc. different angle for different calulation methods.

So, if in this area at this date sun isn't passing this angle values there is no possibilty to calculate time of Fajr and Isha. That's probably an answer.