One thing these type of exercises don’t account for is extra minutes due to games missed because of injuries which always happens.
I went back 2 seasons ago to the 2019-20 season which we didn’t have any roster turnover during the 72 games which makes it easier for this exercise(last season was such a mess), and added up the total average minutes of each player. I came up 320.6 which is much higher than the 240 if nobody misses any games.
For our major core players that season out of the 72 games Hayward missed 20, Tatum 6, Brown 15, Walker 16, Smart 12, Theis 7, Wanamaker 1, and Kanter 14. R Williams only played 29 games. Looking at the games missed I would say this is somewhat the norm for most teams.
For this upcoming 82 game season let’s say we are healthier, and cut the total average of minutes above 240 in half so we are at 280. That’s still plenty of chances for the likes of Kanter, Parker, Hernanngomez, Nesmith, Langford, and Pritchard to get some extra run.