InputDelay and OutputDelay for NARX model

I have been looking through the Q/A posts about determining the number of delays for NARX model; inputDelay and outputDelay.

I'm still confused about the procedure..

If i'm not wrong, target-target correlation can be find by using xcorr(targets).

While input-target cross correlation can be found by using xcorr(inputs, targets).

Next, how do i analyse the graph/results to determine the number of delays?