It may take more than 30 minutes. :~)
This is like deja vu all over again. When Gracie was first broke (10 years ago!) I would put her in side reins and longe her 30 minutes before I climbed on her. She HATED it (and getting her to longe in an open field was an adventure in itself - we kept winding up facing each other, and she learned to run backwards . . . . ) but it was the best thing in the world for her.