Is our prayer valid if we prayed Maghrib at 5 o'clock when the rain was heavy and the sky was covered with clouds, while the next day we prayed it at 7 o'clock because the weather was clear and the sun was shining?

The entry of the prayer's time is a condition for the validity of the prayer. Therefore, whoever prays before the time enters, their prayer is invalid by consensus, whether done intentionally or by mistake, and whether it was the entire prayer or part of it; based on the Almighty's saying: "Indeed, prayer has been decreed upon the believers a book [to be observed at] fixed times." The time for Maghrib prayer begins at sunset. If you prayed Maghrib before sunset by mistake, you are obligated to repeat it, and there is no sin upon you for praying it before its time; based on the Almighty's saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended."