This depends on the content to a large degree. If the content is related, for example, letting go of anxiety and sleeping more easily and calmly you could listen on the same day or the following day. There is nothing to stop you listening to the release anxiety one first and one of the sleeping ones afterwards if you wanted to and you are in bed.
If the issues are totally different it is probably better to separate them out. For example I wouldn’t listen to Stop smoking and Stop biting your nails at the same time. I would be more inclined to let my mind concentrate on one issue at a time. In other words maybe use Stop smoking first and only once that is well established  think about using Stop biting your nails.