Is it permissible to perform the Sunnah prayer of Fajr after performing the Fajr prayer, due to the Adhan being called earlier than its prescribed time?

The prayer times specified in Islamic calendars are correct, including the time for Fajr. The method used to calculate them is not new; rather, it has been the method of Muslim astronomers for centuries. Modern observations have proven the concordance of the adhan time in calendars with the true dawn (Fajr As-Sadiq). The adopted angle for the true dawn ranges between 18 and 19.5 degrees, and all Islamic countries rely on it.