Withdean would be a good call (check times though). The North Lains, Lanes, Pier, i360 would be a good stroll. And meet up somewhere in Queens Road, everyone local knows the clock tower, which is down from the station. 6:00 would be a good meeting time.
Are we missing something. He has a match ticket and a car. Park in centre for an hour or so and then drive to Mithras House where it's free. Then back to the car and into the centre at about 5:30 to pick her up.
One thing I would say, allow TWO HOURS to get to the Amex. You'll want to look...