It can help to mention this issue to the assistants for both teams before the game and ask for them to be alert to help.

Not if teams in your area expect you to use it.

Generally speaking, on the second horn, if teams are making a legitimate effort to get on the floor/to the throw-in spot, I'll hold the ball for a few seconds. If they're still huddling with zero effort, I'll look at my partner, whistle, call direction & point, set the ball down, start counting, and prepare for the high-tailing to the ball.

This season, I've only had one game where this was necessary, and my partner and I had to do it FOUR times. (I've never seen that many.) Surprisingly, they all got it in under the five seconds, and at least two were opposite line.

Has anyone ever had a T after one ROP? If I understand the rule, that's the proper procedure, correct?

I think it's only a T if the team continues to delay during the same event.

That is, you could use the ROP in the first quarter, and again in the second if a team delayed without issuing a T.

7-5-1-c says "Following a violation by one team only, if that team continues to delay when authorized to make a throw in, it is a technical foul."

7-5-1-d says "Following a violation by both teams, any further delay by either team is a technical foul."

Case play on this doesn't give a whole lot of clarity re: further delays by one team only. The rule seems ambiguous as to whether this is all further violations or just subsequent throw-ins related to THIS particular throw in. I'd read it as any further delays during the game but I don't make the big bucks so I defer to those with superior knowledge and experience (pretty much everybody in the world).

Speaking from the perspective of a coach, they don't always hear the horns since they are engaged with providing instruction to their team. So as an official rather than the hover method, I give them a whistle and a flyby and make sure I'm talking to an assistant when I say "get them out on the second". I'm with Jeremey, put the ball down and blow the whistle, preferably when the delaying team has the ball.

I think it has more to do with the fact that in NCAA-M you can give a DOG warning for not being ready to play on the second horn, and the next time they do it it's a Class B to the coach.

The way I understand it...

1. ROP enacted, and Team A is called for a 5 second violation.
2. Team B is given the throw-in, but also is called for a 5 second violation.
3. Team A is again called for a 5 second violation, and is thus given a technical foul.

Mechanic Change?
 

For those following NFHS mechanics, there has been an NFHS mechanics revision for resuming play after a timeout that may not have been mentioned thus far and that might merit consideration...or not. This year's new Officials Manual says (shaded revisions in grey in the text in bold here):

"1. At the warning signal (first horn) for all time-outs, and the intermissions between the first and second and third and fourth quarters, the officials will [U]take one or two steps toward the nearest team huddle and notify the head coaches/benches by raising an index finger and saying "first horn. 2. The officials should then move toward their proper positions to resume play . . . 4. After the second horn to end the time-out or intermission, the administering officials shall found his/her whistle to indicate play is ready to resume, signal the direction of play and announce the jersey color of the throw-in team."

The relevance of any of this I'll leave to others, if it seems worthy of consideration...