PHILADELPHIA — The Boston Celtics have gone from heavy favorites in a series most people in both Boston and Philadelphia thought might be a sweep, to 48 minutes away from their season ending, thanks to the Sixers Game 6 win at Xfinity Mobile Arena .  “Game 7 is a game amongst itself,” Jaylen Brown said after the Game 6 loss. “The rest of the series doesn't matter. It's gonna be who's gonna show up on that day and be the better-performing team. We definitely see some stuff that I know I can improve. Definitely would shift my approach going into Game 7. I'm looking forward to coming out with a great fight." Now we know when that fight will be. The NBA announced late Thursday night that the Celtics and Sixers will play at 7:30 Saturday night, and the game will air on NBC and Peacock. NBA There were a few different windows for this game, but the Celtics got the prime time spot because both the Minnesota Timberwolves and New York Knicks ended their series with Game 6 wins.…