Ah the topping questions...Always an interesting subject to me. First before doing anything, make sure that the strain that you have takes well to topping as not all strains do well with any kind of topping.
I know most of us here do inside grows that are space limited so they need to be controlled to stop them from out growing their space. For that reason and others, we do various methods of training to achieve low growing plants.
I like to top, FIM, and supercrop my ladies and have just gotten into tieing them down as well. I have found the best time to top clones is when they are 3-5 nodes tall. This will give you the "twin towers" effect(not the terrible point in history, but the tall twin colas that will predominate the plant). If you want to create the twin towers higher on the plant and therefore not as domineering of the plant resources, then you can wait and top them 2-3 weeks before switching to flower. This will give you a little variance on the same setup, and disperse the buds a little more.
I like to wait until I have about 6 nodes on my plants and then do the FIM technique. This causes all of the lesser branches that are just budding out from above the leaves to become supercharged to grow up and create multiple top cola buds. Then after Fimming I allow them to grow for another 2-3 weeks before switching.
There is tremendous variation for applying the techniques and I wouldn't say that any one technique is wrong or will hurt the plant (other than applying them during flower, that's a no-no). I have found that I am liking doing different variations on the techniques and seeing how they turn out.
I say don't be afraid to try something, but only use one method at a time until you get used to doing it. And make sure your plants are healthy and growing vigorously before using any of the "high stress training" techniques.