Topping

i have topped at the first node before and the plant has come through and given a great yeild. I would normally wait until the third node is quite well developed. This is usually when you start to see node 5 and 6 pushing. i dont think it matters really if it is week 4 of veg as a way to decide. You need to look at you plant and see what you feel. The more leaf the quicker she will heal. So far for me all my plants have been topped when they are ready. It is not a time period but more when she is ready and strong enough and conditions are good. But thats just me. Good luck.