I have only ever pinched the tops. But since your plant has become overly tall and stringy I would actually cut back at least an additional three inches and try to root that cutting too. You really have nothing to lose. You won't hurt the original plant. And hey that secondary cutting might just root fine.
Keep the cuttings in bright light but not in direct sun.
Keep the established plant/s in bright direct sun. Move outside as soon as possible. I would say not until late May in your area.
