OK ! I find in my 1965 copy of the D&RGW "Rules and Regulations of the Operating Department":
82. (Revised January 1, 1971) Time-table schedules are in effect for 12 hours after their time at each station unless:
1. Fulfilled, or
2. Annulled by train order, or
3. Abolished by bulletin for the life of the time-table.
Regular trains more than 12 hours behind either their schedule arriving or leaving time at any station lose both right and schedule, and can thereafter proceed only as authorized by train order or as provided by Rule 550.
(550 refers to CTC rules)