Conclusion: Performing a freqency sweep response measurement of the digital filter box and taking the derivative of the phase with respect to frequency gives a value of 1.2 microseconds, in agreement with the measurement of logpost 11512.

The digital filter box of one moku pro was set to an all pass filter using the API. The sampling frequency is 39.063 MHz. A second Moku measured the frequency response. The phase data of this frequency response was numerically differentiated using next neighbors, and the delay of 1.2 microseconds is the median time over all pairs.

When the same measurement is performed using a single moku in multi instument mode and the signal is routed through the internal bus, a delay of 950 nanoseconds is measured. 

An independent measurement of the DAC + ADC delay gives 250 nanoseconds. A pulse from the oscilloscope is split, half is routed outside the moku and the other half along the signal bus, the arrival times of the two pulses is then compared.

This leads to the conclusion that the 1.2 microseconds of delay is approximately 950 nanoseconds of filtering time plus 250 nanoseconds of ADC/DAC time.