i don't cut them ever. the center of the tip may still be producing new buds. i have had some bloom for years at a time. if the very tip turns brown and dead, just cut off the dead portion, as the little nodes at the stem segment joints can produce side branches, and usually do after the main stem, stops. or, they could also produce a keiki (baby plant) that you can eventually detach and plant by itself, or int he same pot with its mother.