By Wally Pyrah IT IS twilight racing again in Hong Kong on Saturday, when Sha Tin hosts an exciting and informative 10-race programme, starting at 9.00am. Reigning champion jockey Zac Purton was back in the winning groove with a double at Happy Valley in midweek and looks sure to supplement those victories as he has another batch of winning chances during the action. The likes of newcomer Fast Network, who has had track-work watchers purring in recent trials, lines up for his debut in the Chai Wan Road Handicap (9.30am) over five furlongs, and Super Infinity in the Hong Kong Riding for the Dis…