Salaah

Sitting and performing Fardh and Waajib Salaah without a valid excuse

Q: If a person prays a fardh or waajib  prayer sitting down, without a valid excuse, is his prayer considered invalid? I recently heard from a Mufti that the prayer itself would be valid, since he did not miss a fardh element of prayer by sitting down (and not standing). What is the position of the Hanafi madhab in this regard?

Performing maghrib Salaah half and hour after the time sets in

Q: I started praying Maghrib Fardh about 30-31 mins after Maghrib started (according to the calendar) and finished 41 mins or so after Maghrib started. I am not sure if I performed it on time as it was already dark outside. Do I make up the prayer or is it valid because my intention was to pray the fardh of maghrib? I also prayed 2 sunnah what about them?