I don't know, but for any script with any trigger the fastest way from trigger to shooting is to have the camera (script) wait for trigger shutter half pressed. That way auto exposure & focus are done when arming the remote shutter, not when pressing the external trigger.
I don't remember the actual absolute delays (SDM docs may help, even though they concentrate on syncing the delay of two cameras and measuring the difference between the two, not minimizing and measuring the absolute delay), but it's probably somewhere between 10 ms and 50 ms and for most cameras quite repeatable as long as your CHDK is in the correct remote mode.
