If the sunrise is at 5:20 am for example, Is it the last time of kaza of namaz soubh? I can still do takbir a 5h19 for example? Or I have to finished at least 1 rakat before 5h20?

What is the fiqh law please?

Yes, the qaza time is the same as sunrise timing for Fajr Prayer. If you complete your first rakah and enter in the second rakah before Qaza timing then your namaz is considered 'Ada'.