Some more data pertaining the discussion at hand;

The HT buff appears to activate ~1.75 seconds after initiating the attack. So when determining rotations/priorities it may be worthwhile to keep in mind that the buff does not apply immediately when the ability is used or at the end of the 2.5 (before Skill Speed) GCD.

Maybe this was obvious, but the HT buff does affect HT so reapplying while the buff still persists (if only barely) may be worthwhile.

As was previously mentioned, I was able to confirm that if you initiate an ability with the HT buff (or any buff) up but the animation/damage finishes after the buff has faded you will still receive the benefit of the buff.