What would you have done?

[Nevadaref]

Originally Posted by Dan_ref

Not sure where you're going with this.

The allotted 5 seconds does not begin when the ball falls through the basket.

What B did was within the rules. Game over, go home.

I agree Dan. I'm just saying that as arbiters of The Game (note the capital T and capital G) we have to ensure fairness. We need to be mindful of a team trying to purposely delay for MORE THAN they are allotted. If that wasn't the case here, then game over. No problem. However, we should certainly be on the look-out for it.
Personally, I check the clock when the ball goes through and am looking for a time-out from the trailing team, but in this case they didn't have one, so that wasn't as important.
I also check the clock AGAIN as I start my 5-second count. That way if there is a violation, I know how much time to put back up or if the inbounding team can legally run it all the way out. Perhaps that is my best bit of advice for the OP.