To be honest some people have absurdly fast reaction times and if you're not one of those people then.. there's not much you can do in that department haha (trust me :c ). Having said that, reflects aren't all reaction time - and I'd argue that reaction time isn't even the most important factor. Like many things in TF2 being good at reflects is about reading your opponent rather than simply reacting as fast as you can. Watch their character model and see if they're flailing about - they're probably going to hold down mouse1 and shoot the next rocket as fast as they can reload. I'm not exactly a pyro expert haha but maybe that can help.