Don't sweat about the showdown, it's only 20 targets per course.
Simplest approach is to get everything possible out the way before putting eye to scope. So get in position, get comfy, get loaded, relaxed, pull the strings to make sure you're looking at the right target (ahem), take a punt at the first range, focus the scope, dial it in... get hand over parallax, put eye to scope, if it's a short one, roughly in focus, take the shot. That should see the first shot going out at sub 10 secs, leaving you plenty for the other one.
If the first target is long stick it 5 yds out from what it should so it's visible but not in focus too well... that way you'll find it fast but be roughly in the ball park for final focusing. Get a good range, and send it on that. Don't faff with 2-3 stabs unless you know you're fast.
If you're motoring, both can be down in around 30 secs, but 45 is better for a smoother ride.
The Showdown is as much about not making mistakes and being organised as it is about shooting, and everyone will be as keyed up as you are.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep