Attached is the sign for the locker policy at Six Flags America.
Note the sign says for Superman riders only, however, they aren't sitting there waiting for you to come out of Superman. You could use the locker for the full three hours if you want without paying the $5 per hour "late fee".
Of course, if you don't want to pay the fee, there are alternatives. You could ride another ride, put your stuff in a locker at the front of the park, leave your stuff in the car, not buy a souvenier cup (not sure of the values of these anymore since they are now $11.99 with free refills that day only), wear cargo shorts that have deep pockets, zippers or buttons and stuff your stuff in their (my hat and small camera fit in mine).
Everyone seems to forget, if Six Flags really wanted to rip people off they could go back to charging season parking pass holders parking for each and every park.
Less than .75 per hour seems like a very fair price to me for a little bit of piece of mind and insurance.
Locker Policy