Have any authentic hadiths been reported indicating that the deceased leave their graves on Thursday night (the night preceding Friday) to receive Sadaqah (charity), and that Sadaqah reaches them like gifts on plates? And is visiting graves on Thursday (the night preceding Friday) a Sunnah, or is it permissible on any day?

No authentic or weak hadiths have been found to indicate that the souls of the dead gather on the night of Friday and during the day. However, Ibn al-Qayyim mentioned some visions and narrations from the Salaf regarding this. As for visiting graves, it is permissible on any day, and it has not been proven that the Prophet (peace be upon him) specified a particular day for it.