You set a timer for 28 seconds, and wait to turn it on until your spec recharges to 90%. IMMEDIATELY after it charges to full 100%, flip the 28 second timer on. Cast the first special at about 26-27 seconds and make sure you actually target someone so it uses the 55% spec. If you timed it right, you should get a +10% recharge at the 28 second mark, which is right during the animation of the first spec, which brings you back to 55%. The reason I say cast it a bit early is because if you are early, you still get the +10% recharge (meaning it's spec-hit-spec, which is bad but not terrible). However, if you are even a half-second late, you will have to wait another 28 seconds for the +10% recharge, meaning only one special.
Note: I strongly suggest practicing in the duel arena or on a high-HP monster until you can actually get the timing from spec-hit-spec to spec-spec.