I have yet to find clarification on when exactly the teleportation from the Horizon Walker ranger's Distant Strike feature must occur relative to the actual attack. The description of the feature says (XGtE, p. 42; emphasis mine):
[…] you can teleport up to 10 ft. before each attack to an unoccupied space you can see.
Does that mean you can teleport at any time before you attack? Or must the attack land the moment you appear? (In other words: Does "before" imply immediately prior to each attack, or at any time during your turn before/between each attack?)
For melee, this makes a huge difference, since all 3 creatures need to be very close together if you can't move between teleporting and attacking.
Best Answer
Rules as written, read strictly, indicate that you can move after teleporting and before attacking.
As you've demonstrated, the text for this ability doesn't state "immediately before attacking", so you can indeed teleport, moving then attacking as you would would for any turn where you take the Attack action.
There is clear precedent for the requirement of the word "immediately". Compare this to other features in this D&D Beyond search, each of which clearly indicate either "immediately before" or "immediately after" their respective actions.
Doesn't this allow you to change your mind after teleporting?
Not really. D&D 5e rules don't provision well for promises. Imagine that a Horizon Walker teleports into range of an enemy which has taken the Ready Action in anticipation of this, attacking as soon as the Horizon Walker finishes teleporting. If the attack kills the Horizon Walker, then they can't attack and they've broken their "promise" to attack after teleporting. Most people would agree that this scenario can play out, else it would imply that you could see the future with Distant Strike and use it as an "undo" button.
Under this interpretation, it follows that you simply need the intent to attack in order to use the ability. So long as, to the best of your ability, you follow up on your promise to attack after teleporting with Distant Strike, then you can use it.
The rules probably don't expect you to do this.
The example above is a little tedious, and I think it's safe to say that the designers probably intend for you to attack immediately after teleporting. It's much easier to assume that they made a mistake than to assume the implied existence of a promise framework.