1. Find a new friend ... one that will give you proper growing advice.
2. The natural light cycle for flowering plants is 12/12.
3. If your plants are five feet tall going into the flowering cycle, they will grow approximately twice that high during the flowering cycle. If ten-foot plants are too high for your ceiling ... next time start flowering sooner. For example, I usually start flowering at around 15" and end up with plants that are around 2.5' tall at harvest.
If you only have one plant, you can train it under a screen ... like chicken wire. As the plant stretches during flowering, just keep pulling the bud sites up through the holes in the screen. This is called the Screen of Green (scrog) technique. As each bud site grows toward the light, the idea is to fill the entire screen with but sites.
Vi