2nd Half - Book starters don't match who is on the court

[splitveer]

Boys varsity contest the other night and the second half begins. About 30 seconds into the 3rd quarter the Home team requests a timeout because he doesn't like the matchups he has on the court. After the deadball the bookkeeper says the Home team did not start the second half with who they put in the book before the half started.

Is this a wrong starter in the book and a T is assessed?
Or
Does the 5 players become legal when the 3rd quarter begins and we play on?

Also, would this be different then the beginning of the game?