Postulating here, not theorem-tested.

Ad copy says “Standard delay time from 10 seconds to 10 microseconds”, and “modulation sweep from 1/2 to 2x the standard delay time.”

So, that would be 0.05-0.2 Hz. at 10 seconds.  The delay multipliers cut the sample rate.  I don’t recall if/how that plays into the modulation speeds.

And on the lowest end of the delay scale, I doubt the modulation sweep exceeds the nominal sample rate (100K).  But who cares about any inexactness down there?  That is the delay area where those gorgeous modulation sweeps live & breathe.