Pupillometry: how long needs the pupil to respond towards an cognitive stimuli? I would like to know if somebody could give me some references on the latency of the pupil response after a cognitive stimulus.

I know that the light reflex is quite fast compared to cognitive stimulation, but I could not find more information than this. Does anyone know how long it takes the pupil to react toward a cognitive task? Or a good reference where I could read it on my own?
What are you trying to do?  If you're trying to leverage pupil-dilation data from an eye-tracker, there are ways to deconvolute the timeseries if you can make a strong inference as to exactly when the stimulus of interest took place.

I think you'll find everything you're looking for here.