The Horsham service has about a 3 minute window in which to service Platform 3 at Gatwick. The FGW service arrives at platform 3 at xx50 and vacates it to the sidings at xx53. The Horsham service arrives at Platform 3 at xx55 and departs at xx56. The Horsham service needs to have cleared platform 3 by xx59 to allow for the FGW train to return to Platform 3 at xx01 for an xx03 departure to Reading.