As long as the roots have not really settled & started to actively grow fertilizer does not do anything. It is better to wait with fertilizer until the tree has shown signs that the roots have taken hold.
100% agree with that. A plant will only absorb as much nutrients as he requires. Giving a plant too much fertiliser will only result in a build up of harmful salts in the soil. As a tree is hardly growing after its repot as a result of shock it does not require any fertiliser. The natural nutrients in the soil are enough to feed this tree until you see new growth appear.
In addition: According to Liebsig's law off the minimum, the amount of nutrients that a plant is able to absorb is not controlled by the total amount off resources, but by the scarcest resource. This means that giving a plant an overdoses of phosphorous or nitrogen won't do any good if the scarcest resource is for instance iron. This is why you should always give your trees a balanced fertiliser which is optimised for the plant its needs.
@kittyvlekkie: Hi kittyvlekkie, welcome to this forum. It's nice to see that you have found yourself a new hobby. I hope you will enjoy bonsai as much as I do and for as long as (or even longer than) I do. Bonsai is a very intriguing hobby because there is so much that you can, and have to learn in order to be able to do it right. You'll have to understand advanced aesthetics as well as in-depth knowledge of plants and gardening. Many of us have been practicing bonsai for years and they still don't know everything. As a matter of fact, I think I started with bonsai when I was just about your age too.
I see you are very eager to learn, which is good! Just bear in mind that you are just a beginner and there is a lot for you to learn. There is a long road ahead off you and you'll probably kill a few plants along the way (I know I did). So I strongly advice you to reed as much as you can and absorb as much as you can and keep asking questions. I'm sure we will be happy to answer all off them.
But please, stop giving advise to other people until you have a lot more experience! At a forum like this it's very hard to recognise a beginner from a pro. Writing 100 posts in one month does not yet make you a pro even when this forum tells you so. I think you wouldn't be so happy too if you where to follow someones advise and it turns out to be wrong.