Of course it is about 13 miles long I’m sure and can take around 30 mins Calling at Waterloo east - London Bridge then Orpington but some stop at hither green- grove park- elmstead woods-chislehurst-pets wood and then Orpington but most go though to Sevenoaks or tunbridge wells
Could I suggest to Sevenoaks (22 miles) or even Tonbridge (30 miles) as it's still within the realms of current route length but you'd be able to drive a greater variety of services? Not all fast services stop at Orpington and stopping services sometimes continue to Sevenoaks. It would allow for more complete routes as well as fast and semi-fast services direct to Sevenoaks and potentially on to Tonbridge (which is a meeting point for several lines in Kent). Hope I haven't offended anyone