How soon should you add new yoga moves?

Um I am less then formal and structured. I listen to what my body finds comfortable so I rarely start out with too many modifications.
Occasionally I push it. Not quite that limber hold it for half the time I am happy and will try for longer tomorrow. If I am bored I ramp up the difficulty or throw in something not necessarily in the books or on the screen or whatever. I used to be terrified to do this. Always following everything to the letter then I found this great instructor who encouraged free style.

Best thing that happened to me in yoga.