A RedBox movie rented through the RedBox Kiosk must be returned by 9:00 PM the next evening otherwise if the RedBox movies is not returned by 9:00 PM the next evening then when you return the movie you'll be charged for another day of movie rental.
So as long as you return the RedBox movie to the Kiosk by 9:00 PM the next day you'll be okay and not charged another rental fee.