Why do you think changing the trigger pull weight will help you take a second off of your time, especially since there are no multiple shots on any target?
lowering your trigger weight may help the feel of the trigger itself, but it wont cut a half second off your time. Work on target transitions and being able to get the shot off sooner when you get your sights on the target. (this is assuming you dont miss targets and waste any time there. If you aren't shooting perfectly clean, work on that)
What is your average draw time to first shot? I know it will vary depending on target size and distance, but a slow reaction to the buzzer or a slow draw in general can kill your times something fierce too.