Is it permissible to delay the intention for ghusl until during the shower?

The time for the intention (niyyah) is at the beginning of the ghusl, because the time for the intention is at the beginning of the act of worship. Some scholars have permitted advancing the intention slightly before the act of worship. So, if you remember the intention for ghusl before starting it, or a short time before it, then you should make it. However, if you have washed part of your body without intention and did not rewash it after making the intention, then the ghusl is not sufficient. The intention is merely the purpose of the action, and its place is the heart.