It applies to the initial hit, or at least it did when it first was changed to its current form. I tested it on and was using it with a DK heavy attack build for awhile.
Legendary Archer of Valenwood
Bosmer Dragon Knight Archer. XBox One. (Flawless Conqueror Bow/Bow)
Bosmer Nightblade Archer. Xbox One. (Flawless Conqueror Bow/Bow)
Bosmer Sorcerer Archer. Xbox One. (Flawless Conqueror Bow/Bow)
Bosmer Warden Archer. Xbox One. (Flawless Conqueror Bow/Bow)