How do we calculate the time of the Fajr prayer? Is it when the sun is at 16 degrees or is it one hour before the time of sunrise? Would it be possible to get a source on this matter?
You need to refer to the experts in your area who have authentic evidence on the time of Fajr.
If you can not find such trusted experts,bayou should practice precaution (Ehtiyat).
We don't pray any obligatory prayer before being sure that the time has started.
Wassalam.