Time limit to cut short before length limit: Theoretically interesting, you could even make shadows that compute this -- but I fear that this is much harder to plan for both creator and player. I would stick to a length limit, then you can have rulers, too.
L2 beam extends in steps, once per second, cutting through air instantly in one step, which still looks like it's non-instant. I suppose you want to extend the beam every frame, in smaller steps. At least I recommend to extend every frame in smaller steps, unlike L2.
I'm 50:50 whether we should cut through air instantly, which physically makes sense for a laser, or merely faster than through terrain, e.g., 6 diagonal pixels/frame, because in video games, laser beams are fat and travel in slow motion.
-- Simon