Toping flowering plants

I am 14 days into flower but my plants have grown into the lights i want to know how late into flower can top them. I have tryed to bend them over but they are growing so fast they keep growing into the lights

Look up super-cropping, I've done it as far as 3 weeks in with no problems. I don't like to once into flowering but in a pinch it's about the best way to handle it.