The Fisher-transformed values of r are first multiplied by "sqrt(N-3)", where N is the number of time points, and then that value is ceilinged at 15; note that since the @ROI* script uses the log-form of the Fisher-Z, it also puts doesn't let the denominator be zero, having a tiny perturbation away from r being too close to unity. The 3dcalc-like expression is (here, the correlation value is represented by 'a'):
-expr "min(0.5*log((1+a)/max(1-a,0.00001))*sqrt(${N}-3),15)"

The "sqrt(N-3)" factor is the inverse of the standard error of the transformed variable (i.e, the standard error is "1/sqrt(N-3)", where N is technically degrees of freedom, which would be less than the number of time points if you have processed/regressed stuff out). See the discussion thread here for more:
[afni.nimh.nih.gov]
I don't know that it would be generally desirable to multiply by this factor, actually.

If you want just the standard Fisher-transformed Z-score, perhaps, "3dNetCorr -fish_z ... " would be the way to go. Note that the Z-score values there are presently ceilinged at 4 (corresponding to r=0.999329; in older versions, it was higher, but it shouldn't matter for time series, where the correlation is typically muuuuuuch lower than even Z=4).

--pt