hi Mingbo and Gang
I have tried to do this as well and it did not work for me either. Specifically, the SPMGx basis functions do take an optional duration argument, but this cannot currently be used in combination with -stim_times_IM (though it can with just -stim_times), while say dmBLOCK can be used with -stim_times_IM.
I don't know how much work it would be to make 3dDeconvolve allow the use of SPMG1 with -stim_times_IM, but it would be useful for me in some teaching-type situations.
James