This is optimal. First I make the first mini hit Donkey Kong as soon as possible. This will cause the second mini to spawn as soon as possible. The third mini however will spawn due to how much time has elapsed because it's impossible to hit Donkey Kong before it spawns. With this in mind, it doesn't matter how fast the second mini can hit Donkey Kong. Just as long it hits Donkey Kong before the third mini does. You want the third mini to hit Donkey Kong as fast as possible and the fastest way I found is by making it take the ladder on the left as its a shorter distance away than the ladder on the right.