I agree, only I feel that with the polearm nudge I find myself getting hit by it closer to the end of the wind-up part of the animation than when the polearm is actually thrust forward, if that makes any sense.
To try and better illustrate what I mean:
Steps of the polearm nudge animation (when starting from an up block position):
1) Bring weapon back and down to chest level following a roughly-circular path.
2) After roughly 3/4 of the circular path has been completed, the polearm is more or less directly underneath where it was being held in the up block. <-- This is where the collision currently seems to happen.
3) The polearm is now thrust forwards. <-- This is where the collision should happen
4) The polearm is retracted in an animation that seems like a reversed version of the forwards animation.
Looking at a step-by-step comparison of the shield nudge to the polearm nudge animation above, here is what the shield nudge looks like:
1) Shield is held exactly where is was whilst blocking, however shield is now not able to block anything. <-- The cause of "delay"
2) Shield is thrust forwards, hitbox is active on the earlier side of this part of the animation.
3) Shield is left dangling in space, hitbox is no longer active.
4) Shield is quickly brought back to the blocking position (usually because whoever did the budge is still holding RMB).
So while the animations seem to have the same duration, the shield nudge has more "dead time," or delay, as you mentioned, which accommodates for the extra time the polearm nudge takes to "wind up."
Basically, if you could shave off some of the "delay time" for the shield nudge, and then push back the active hitbox time for both nudges*, then these two nudges should be easier to land since they will be more intuitive.
*By push back I don't mean to extend their effective time, only to make it start later and last the same amount of time. For example, if you are going to punch someone/thing, you don't line up the punch so that they are at point-blank range. You position yourself so that after bringing back your fist, you have the time/space necessary to fully accelerate your fist for maximum power. As it stands, the nudges are hitting people "point blank" as opposed to later in the animation, when the actual "pushing" motion is being done.