Timetable 2nd/3rd class schedules were authority to run, not necessarily ,usually, the actual times at given points. On SP there were three 3rd class freight schedules per 24 hour day, to be used by a DS to run one train , or several sections of a train. Check the rulebooks for mention of restrictions that forbade trains leaving a schedule point before specified time.. "Run Late" orders could be, and were, issued to interested parties to avoid large delay in waiting for a train using a schedule. Also provided were orders that noted annulment of all or portions of a daily schedule.
In other words, SP schedules provided a framework for the DS and not necessarily precision. Coast Second class schedules, such as the Overnights, were more precise when the Larks et al preceded them, and precision was required in order to make the meets in CTC and double track near San Luis Obispo. Third class freights had to clear those times where ever a siding was available depending on actual conformance to the third class schedule , or per claifying order from the DS, such as "train XXX has right over XX from A to B, accompanied by "until... " and " wait at...."
Running by TT and trainorder did not necessarily mean precision running of freight trains, nor multiple sections of first class passenger trains