I have two Great Northern condensed timetables for the summer of 1965, one that was “effective May 23-September 6” and one “effective August 22-October 31.” The only substantive difference I can find is that, on the earlier timetable, train number 20 from Minneapolis arrives in Duluth at 7:05 pm, while on the later timetable it arrives at 7:00 pm.
Beyond this, there is another curious difference: the earlier timetable shows all schedules in both standard and daylight time. But many of the daylight columns are blank or mostly on the later timetable. Daylight times are completely missing from the Winnipeg Limited, Red River, and Dakotan schedules, and except for Superior, Wisconsin are missing from the Badger and Gopher schedules as well. Perhaps for lack of room, neither timetable has daylight savings times for the Havre-Great Falls route, but both have them for other trains.
Though the railroads invented standard time, they did not invent daylight savings time and were not enthused about it for many years because it wasn’t uniformly observed by the various states, which made timetables even more confusing. For many years, trains ran on standard time in states that observed daylight time, which meant many people would show up an hour early for trains–which was at least better than being an hour late.