The true intent and purpose of § 28-11-2 — § 28-11-4 is declared to be to limit the usual hours of labor of the conductor and operator employees of street railway corporations, in the absence of agreement as to hours between the employees and their employer, to ten (10) hours actual work a day, to be performed within a period of twelve (12) consecutive hours, whether the employees are employed by the trip or trips, the job, the hour, the day, the week, the month or in any other manner. Nothing contained in this chapter shall be construed to forbid or prevent any employee, being eighteen (18) years of age or upwards, from laboring a greater or lesser number of hours a day in accordance with his or her contract to do so, nor to impose any penalty upon any person or corporation for permitting these employees to labor a greater or lesser number of hours in the performance of the contract.