Isn't the time for Fajr prayer too late if it is performed 40 minutes before sunrise? And is it permissible to pray at home and then repeat it with the congregation in the mosque?

The Sunnah regarding performing the Fajr prayer is to pray it early, while it is still dark (taghlis). This is the view of the three Imams: Malik, Shafi'i, and Ahmad. Delaying the Fajr prayer until after the light of dawn spreads (isfar), without a valid excuse, goes against the Sunnah. Whoever finds that the mosque delays the prayer until after isfar may pray at home and then repeat it with the congregation to combine the virtue of praying at the beginning of its time and praying in congregation. The mosque community should perform the Fajr prayer according to the authentic Sunnah, which is taghlis.