Must I stay in Mutianyu for 5 hours?

Hi. I want to visit Mutianyu. Can I get to any shuttle bus I want in Quianmen, stay on the Wall AS MUCH AS I WANT (e.g. 2 hours, 3 hours) and not 5 hours obligatory, and then take any shuttle bus from Mutianyu back to QIanmen? Or staying there for 5 hours is mandatory and I can only take back the same bus? (which I don't want). Thank you.