The two Fajr Sunnah rakahs are offered after true dawn and before the Fajr fard; they are not performed in the prohibited interval at sunrise.
Where the Sunnah was missed, jurists distinguish its makeup: Muhammad preferred making it up after the sun has risen and before noon, while another Hanafi view does not require a separate makeup for the Sunnah alone. Missing the Sunnah together with the Fajr fard involves a separate ruling.