In-game description of Riposte:
Blocking just as an enemy attack is about to hit causes your next melee attack to be a guaranteed critical hit.
There’s no information about duration of this talent in description.
When this talent is triggered, if player doesn’t attack within 2 secs, there’s no guaranteed critical hit of next melee attack. So, is it intended that WHC Riposte only works within 2 secs after being triggered?
Definition of riposte
a fencer’s quick return thrust following a parry
I’d guess it’s intended to work that way.
I didn’t know that. Your replying makes sense. 
Definitely seems like something that ought to be in the talent description. @Fatshark_Hedge Any official word on if this is intentional?
It’s as easy as stand in front of them and use the light attack after you’ve parried.
Description needs clarification, we’ll sort that.