The reason Southern can claim that 90% of the trains are on time is that the figures only relate to a proportion of their total services. They only have to refer to the punctuality of peak hour trains arriving within five minutes of their advertised arrival time. Peak hour trains are those on Mondays to Fridays arriving in London between 0700 and 0959, and departing from London between 1600 and 1859. So no off-peak services count at all, and neither do less popular commutes such as away from London in the morning and towards London in the evenings. Even with the peak services that do count they have got over this over the years by adding extra time onto arrival times when they produce new timetables. I can remember not many years ago all the stopping trains from Forest Hill to London Bridge were timetabled to take 12 minutes. If you look at the latest timetable practically every rush hour train into London is timetabled at 16-17 minutes! The journey hasn't got any longer but it gives them extra minutes to play with in addition to the 5 minutes that a train can be late before it is technically late!That 's why when a train is on time it often has to sit outside London Bridge for 5 minutes!