Question
how long do i have to wait to cut the bananna from the tree?

Answer
Mario,

From this question I am assuming that you have a banana tree with fruit.  

You should wait until the skin starts to turn yellow and then pick from the tree.

This is a greatly different situation from the bananas we buy from the store.  Because the fruit will bruise so easily they are picked green, shipped, and then exposed to the plant hormone ethylene which aids in the ripening process.

Gary