Oh dear, Southern aren't having a great time at the moment, the consultation on their 2018 timetable should have started this week, first off there was a holding note saying that it would start Friday due to the strikes, now they are having technical problems:
http://www.southernrailway.com/your-journey/timetable-consultation
http://www.southernrailway.com/your-journey/timetable-consultation
We are very sorry but due to a technicality with one of the interactive documents, we have not been able to start the consultation yet.