well now that I think about it we will probably wait until we have alternating nodes as well. There's nothing too scientific about topping. When the plants are mature enough topping is recommended just a few weeks before going into flowering. By most time tables this puts topping right at or around the 4th week *or waiting until alternating nodes appear which should be right around this time as well. We plan on topping then letting them veg for at least another week after.