Well my guess is this, it ENHANCES velocity shot giving it a boost. The description below comes from wiki so the info is there, if it enhances VS then it would do just that...reduce the delay on ranged and raise damage already recieved via VS. How much more? idk there doesnt seem to have been any testing done. Its most likely a few % tho.

Velocity Shot

Job Ability
■Increases attack power and speed of ranged attacks, while reducing attack power and speed of melee attacks.
■Obtained: Ranger Level 45
■Recast Time: 5:00 minutes
■Duration: 2 hours
Notes/Description
■This ability can be activated all the time because of the recast and duration time.
■This ability will wear off if you zone while its active.
■This ability is not available when Ranger is set as Support Job.
■Ranged Attack + 15%
■Ranged Attack Delay -10%
■Attack - 15%
■Attack Delay +10%