A. The strength of the concrete in this retaining wall is only one small piece of the larger puzzle. Soil conditions play a large role in how much of the vibration energy reaches the wall. The water content of the soil also can have a large effect on the interaction of the various elements in the system.
I can’t tell you at what point in time the concrete strength is no longer the limiting factor. But my best guess is that waiting until the fifth day or the 90% indicator should be sufficient to have passed that point.