My white widow last grow got flipped when they were at 17" tall. I had fimmed all 4. After the stretch the tallest got to 44", the shortest was at 40".
Just want to be sure you have room for the lights above the plants after they finish the stretch.
Ya I think your idea of topping them and giving them a week to recover before flip is solid. Better safe than sorry.
I hope you are keeping notes along the way. It will be a great benefit on your next grow.