I accept it's nice to have trains leaving on time, but they have been leaving earlier than 30 seconds before the scheduled departure time, particularly the 8.00. One instance a few months ago the doors shut and the train pulled away as the station clock was still showing 7.58, which took me by surprise as I was casually walking up the platform towards the end of the train! I used the 10 minutes waiting for the next train to e-mail a complaint to Southern and got sent a refund voucher, as well as a note saying that their drivers had been instructed to hold the trains if they arrived ahead of time. They did this for a while but seemed to have slipped back in to old habits recently, so it's worth raising it with them directly.