There’s two spans, if the size of container is enought to acomodate both in the same line, the second span floats to the right, if not I need the second to be bellow the first.
A <span> is an inline object, so you might not want to do that at all.
What you probably want to do is give a block element (eg. <div>) a float: left and float: right along with a set width. When they meet up they will automatically pop down.