Here's our mechanic when dealing with no huddle offenses (and we have many including our conference winner). The U always starts over the ball if the no huddle team is on offense to be signalled off by the R if:
1. A does not sub.
2. If A subs, R holds U and signals with both arms out, looks to B for a short time - if B doesn't sub, R points U off and we go - if B subs, then R waits until B subs are basically ready then points U off.
3. Sometimes, A will first sub, then bring another sub in, and we have to bring the U back up and hold a second time.
4. When the R is signalling, so do the wing officials.
It works great and all our coaches know what's happening.
I thought this was the national mechanic?
PS: one team in the BCS big one never huddles and goes very fast!