Stay behind for a leisurely pint, amble down to station, wait five minutes or so, board train. No problem.
To Brighton . . . Worst case if you clap all the players off , then slowly walk to the station is a 15/20 min wait.
If you wait 15 mins having a pint or whatever then you will more or less get straight on one
It's quicker to get to Lewes as it's the first stop, whereas the train to Brighton stops at Moulsecoomb & London Rd before it gets to Brighton.
Seriously, look on the screens in the concourse after the game as the times of trains are listed, guage the queues, and take your choice.