Two pila volleys in 5 seconds method
To get a fast initial start the units have to be in "ready" state.
Press halt when urbans have raised the pila, otherwise they won't throw the pila
Though in general it's possible to just press halt to skip the "reloading" state even with regular attacks that will add some delay, which is what the testudo formation toggling was for.
Doesn't work with other missile units, requires a different technique.