According to Acts 20:7,
And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight. (KJV)
Ἐν δὲ τῇ μιᾷ τῶν σαββάτων συνηγμένων τῶν μαθητῶν τοῦ κλάσαι ἄρτον ὁ Παῦλος διελέγετο αὐτοῖς μέλλων ἐξιέναι τῇ ἐπαύριον παρέτεινέν τε τὸν λόγον μέχρι μεσονυκτίου
early Christians used to assemble on the first day of the week. But, was this assembly on Saturday night, since Hebrew calendrical days were reckoned from sunset to sunset? Or could the Gregorian calendar have impacted the way this verse was translated since it was the standard calendrical system when the King James Version was published?