Performing Salaah in the forbidden time
Q: As I live in a city and because of the buildings, I can't always see the sky openly. How can I determine that time when salah is forbidden? Is there any trustful program to use, do you know one? I hope it is the one that shows time as salah calendar as I don’t always have wifi on at home? And also, if I didn’t make my fard yet and the forbidden time started, can I still make my salah if I see that due to some reasons I will miss it - like toilet is busy, water is going to be off, etc? How sinful is it to make salah at this time? Also, if I start salah some minutes prior to this time and ended it when this time has started, do I have to repeat my salah?