Best time/height to start to trellis or net?

I would advise using the trellis net before the pre flowering stretch. That way when the plant stretches you'll be able to make that growth horizontal. I also think lollipopping the plants would be a nice thing to do as a next step after the trellis net. - This is pruning everything below a certain height of the plant to make overall bud quality increase in the upper canopy. Good luck ;)