Clocking in to change

I'm a traveler in Ohio in the OR. Everywhere else I've been ( traveler or permanent) th staff was allowed to punch in 6 or 7 minutes early to change and get to the desk for assignments. My current place allows permanent staff to punch in 6 min early and then change. Here the travelers are told to change and wait to punch in NO EARLIER than 3 minutes before start time. Can anyone answer this question and site the source for facts- isn't there a law that says that if you have to change the employer must give you an appropriate amount of time to punch in and change because it's a part of preparation for work? Remember this is specific for Ohio.