Have you scheduled your surgery? if you're not going to go undersurgery very soon don't waste too much time. Tissues have their own flexibility and for the most it's genetic and due to your age. Don't do it too hard, it's not necessary and you risk to rip off.
Stretching is important during the lenghtening to let muscles and tendons get longer well, otherwise it's not so useful because tissues tend to come back to their original lenght very quickly.
I know that it's a way to feel like you're entering the LL procedure, but it's not so useful. Do it if you like it as fitness activity.