Much easier to find out from game management where the teams come out on to the court from and the two umpires can position themselves to make sure the teams straddle the side and go directly onto their half of the court. Try to avoid starting the game with a T. In Pennsylvania, we are asked to be on the floor prior to the teams arrival.

It's not even a request here, where following a JV game, the varsity squads are typically shooting layups before the JV officials even get to the locker room to tell the varsity crew the game is over.
15 minutes is the standard for taking the court.

Frankly, that's how I think it should be handled.

Very similar to dunking or any other "unsporting" act now. What happens when both teams are on the court at 20 minutes, and B12 and A4 start trash talking across the division line? Nothing, because the officials aren't there and aren't required to be there.

So, it a team runs a lap at 20 minutes, it's "wrong" (and a fan or the opposing coach could write the conference / state), but there's nothing for the officials to enforce. IF it happens at 15 minutes (or whenever the officials get there), then enforce it.

Since all players are bench personnel during warm-ups, couldn't a bench technical be called in this case? The Bench T would then be an indirect on the head coach.

Well, lacking direct instructions from your local governing body, we could also follow the directions from the NFHS POE that I cited 3 days ago in post #8 of this thread. It's still valid afaik.

From POE #3 in the 2002-03 rulebook re: pre-game situations:
"The specific inappropriate actions of a few team members may be individually penalized or the entire team may be assessed one technical foul, if they collectively engage in any inappropriate behavior(s). Since all team members are considered bench personnel before the game or during the game, the head coach would also be charged indirectly with the technical foul(10-4-1d; 2-8-1)."
Note that the rules cited to back that POE haven't changed to date. That's good enough for me. I've got something in writing to cover my azz if I follow that POE, not an "opinion".