You can choose to force yourself to remain in the form of a dragon for a longer period of time.

Prerequisite(s): 7th-level dragon disciple

Benefit: Whenever you take the shape of a dragon using a form of the dragon spell (of any level), you may choose to double the duration of the spell when you cast it. However, if you do, you must remain in the form of a dragon for the full doubled duration of the spell. You are unable to dismiss it.