When you perform a multi-point measurement using the DMM driver, the analog hardware in the board generally takes some time to settle before returning an answer. For instance, you may find that the first measurement takes 3 seconds, but that if you wait 4 seconds the board may return as many as 20 measurements.
This initial delay is the time needed for the ADC, instrumentation amplifier, and RMS converter to settle to stable values. This sort of delay is typical on all precision DMMs which perform multi-point measurements. In general, AC measurements take longer to settle than DC measurements. Also, the settling time will increase as the measurement resolution goes up. Initial delay times range from less than one second for DC measurements at 3.5 digits to 5 o
r 6 seconds for high-resolution VAC measurements.