For the purpose of stimulating muscle growth it isn't a good idea to produce maximum possible power with a fresh well rested muscle.
In an exercise which consists of twelve rep's the first rep should not be performed at maximum possible speed but smooth and controlled, it's not until the final few sets you should be moving as fast as possible but the speed will in fact be quite slow but producing ten times as much power.
The first few reps of a properly performed set will include a so-called warmup, any extra time spent is a waste of energy wich is counterproductive to being able to produce as great as possible power to the final few most productive rep's of a set.