Chrenedict's gives the target (not necessarily only the caster) skin similar to that of a troll. The resulting troll skill lasts until the spell is worn away from damage, and is not dependent on time. The spell will absorb a number of hits, each hit wearing away the troll skin until there is nothing left.

Being troll skin, it only absorbs the blows of weapons that do sharp and pierce damage, and also damages those weapons as a troll would do. Any blunt hit is not absorbed, and is thought not to count towards wearing the spell off. A minor note is that the spell does not appear to stop poison from entering your system, even if the means to inject it is. The main example of this is the giant spiders of Gloomy forest.

 

The amount of 'layers' of troll skin that the caster will receive with a single cast is dependent on their skills. With good skills, in excess of 20 hits should be absorbed. The spell can be cast subsequent times on the same target, but with greatly diminishing returns for the guild points and components spent. That is, each successive cast will add less layers than the one before, and most will find their skin not getting harder at all from the third cast onwards. The total limit you can reach, and the amount dropped at each successive cast likely depends on your skills.