from my understanding they open with a peak then hold, and then reverse to "push" closed,
but the total injection length would be about 5 ms at high loads. and probably 500 ns or less at idle.
so they are high current but for a very short amount of time. since the start and finish of the fire needs to be with in a few degrees of tdc.
Our understanding is different (though it could be wrong): piezo injector drivers don't use anything like solenoid injector peak and hold drivers. Since the piezo elements behave like a capacitor, the current draw is naturally high before exponentially tapering off. You do, however, need to limit the rate at which the load charges and discharges (we've seen either 10A maximum draw or 180uS minimum charge/discharge time). Once the injectors are charged, they hardly require any current.
Piezo injectors also need to be driven with much higher voltages than solenoid injectors. 60V definitely isn't enough; 120V-140V seems like a more common voltage. You're right in that the pulse is usually split between two polarities; the H-bridge handles this task nicely.