Articles generally say waiting till the 5th node to top because of root development. Once you top, it sets the plant back ever so slightly as it recovers and resumes normal veg. It's said to wait till the 5th node to allow for adequate time for the plant to become established, thereby reducing the 'down time' from topping. A larger, healthier plant will recover quicker then a smaller less established plant. Obviously.
If the plant is healthy, it doesn't matter. You can top it after the first node growth if you want... It all depends what your end goals are.... Theres all kinds of diff methods and practices people use so sometimes topping at 4 nodes is better for someone and topping at 5 or 6 or whatever is better for someone else growing a diff way, or not topping at all and just bending it over....