It's an old trick that most railways do to keep arrival times predictable at the busiest stations, at the cost of having them fluctuate more at less important stations. Instead of padding the schedule evenly between all stations, the schedules going away from a major station show unpadded, or lightly padded times for the first few stations, and then on the last leg before another major station they insert all of the padding that was omitted from the ones before it. This way, all of the padding can be kept on hand for a delay anywhere on the line, not just at the beginning of a trip. GO does this on all lines both at Union and at the suburban endpoints.