RULE 24. LAYING OFF-REPORTING FOR DUTY. (a) A yardman will be required to give notice of his desire to lay off at least 3 hours in advance of staring time of his assignment, except in case of sickness, when sufficient notice must be given to the proper officer of the railroad so that extra man may be notified in time to prevent engine working short handed.

(b) Extra yardmen will not be required to report for duty if provided with telephone, but will be called as nearly as possible 1 hour and 30 minutes before beginning assignment.

(c) Extra yardmen will not be marked on vacancies at the time the board is marked up, but will be called as nearly as practicable 1 hour and 30 minutes prior to the starting time of the shift on which the vacancy exists.