Well, wrong. I don't think he figures to have any playing time at all, because thats probably not why they'll sign him.
According to all reports immediately at the start of Bynum's Free Agency, Indiana was only interested in Bynum in order to keep him away from Miami. They understand that Hibbert kills that team and want to keep anyone, even Bynum, away from the Heat. In all likelihood, Bynum is ring-chasing and looking for money over playing time - just going through the motions. It appears he wants to keep milking his career over expanding it, and Miami and Indy must be his top choices.
Now, if Bynum signs for the minimum, shapes up, gets some minutes and plays well, then maybe Mahinmi becomes tradable because his contract is a little large although he is playing great at backup Center. Many possible rewards for Indy as a result of a precautionary move.