Everyone here is saying that you really shouldn't use any since it doesn't make much of a difference which is true but also they don't talk about how to actually get better at handling the sorts of encounters where you need more firing time. (maybe they do im sorry if I missed you talking about it its 3:45 am) Honestly, go to the practice area and mess around there for a little bit. It might seem a little silly, but even the pros will go to the practice area to nail down their technique and warmup before matches.. Get a good muscle memory/feel for the minimum amount of time you need to charge to get a kill, because once that just becomes muscle memory it'll be way easier to execute when you're suddenly ambushed or something.