The problem with the retiring and renewing motion in Rome HBO, is that it would be foolhardy to attempt such a huge undertaking when the enemy was right there. From what I've read, and what little mock combat I've done, in fifteen or twenty minutes it's necessary to take a break. Both sides would be laboring under the same physical limits, with this generic exception:
Most of the "barbarians" that fought with the Romans were lightly armored, so they would not be as encumbered, but they were not professional soldiers.
The Romans were used to wearing their armor and marching all day, so they were more accustomed to the strain and weight, but nevertheless, people get tired when doing physical combat.
If the enemy were right at the line, it would be unlikely that anyone would hear the hypothetical whistle. Nobody really knows how they signalled advnaces, flanking, controlled retreats, or other combat maneuvers. We know they used standards and different horns, but we don't know what kind of signals produced the results. An educated guess is that there would be a switch of the first couple of ranks when the enemy fell back to grab some air, but how that was accomplished is unknown. In Rome HBO, the command to rotate the ranks came after thirty seconds. During that switch, with the enemy soldiers only five or six yards away, there would be an immediate rush, and the crowded lines of moving men around would be incredibly vulnerable, seems to me.
But it looked cool as all getout to see that overhead view of the troops moving. If anybody could pull that off, it would be the Romans. Sadly, there aren't any surviving drill records from the Republic, and AFAIK, none from the early Empire. Maurice and Vegetius are about the closest thing I can think of, and they are from later time frames.