[Imp]

Well try doing it yourself if thats what your preference is.

For plotted fire both the caller & the unit firing have an effect on the lead time so try fiddling to get what you want.

I think experience is the main criteria for call times possibly linked to a degree to arty skill so open up the editor & adjust some mrtars till you get the effect you want then go to the OOB editor & make yourself a custom OOB with those adjustments.

I would suggest starting by increasing the mortar experience by 10-15 points & seeing what happens.