I'm not sure what you mean by "out back" but I'm going to guess you mean outdoors. The dualing tree would be pretty dun for 2 people to compete against each other (although make sure of minimum distances to avoid ricochets).
For indoor ranges, I used the target with 5 numbered targets and try to shoot them as quickly and accurately as my shooting partner calls them out. I'm sure a timer would make it much more competitive rather than "guesstimating" the time it took to get your shots off.
The ATF should be a convenience store instead of a government agency!