I have analysed my record of 13 AM Peak trips from Welwyn Garden City to Blackfriars, since the new timetable was introduced. These have taken an average of 1 hour 16 minutes against a new timetable expectation of 1 hour and 3 minutes (itself an increase of 3 minutes over the old timetable).
Of 10 PM Peak trips for the return journey (excluding days when I have done something different on route home). These have averaged 1 hour 23 minutes against an expectation of 1 hour and 4 minutes (an increase of 1 minute over the old timetable). Two of these trips have ended up with me walking from Welwyn North back to Welwyn Garden City due to 2C55 1744 Cambridge North to King's Cross being reported as on time leaving Cambridge North, only to be very late leaving Cambridge. I can do this in circa 30 minutes, but generally the walk through Sherrards Park Woods is nicer, although it takes about 10 minutes longer - I don't hold GTR responsible for that at least...
This additional time adds up to 6 hours and 5 minutes across 22 journeys (32 minutes per day), on top of the expected 46 minutes (4 minutes per day) that the new timetable 'planned' to impose. Better information would help, I can think of at least seven occasions when I could have done the journey more quickly if I had had accurate information about what was running when I set out...