The Midsummer Sun cobalt inquiry has been put back two weeks at the request of two people charged in the affair.
Vet Dr Tom Brennan and harness racing identity John Camilleri both asked for the delay via legal counsel.
NSW stewards have rescheduled the opening day to Monday, August 3, and it will run for four days.
Sydney trainer Sam Kavanagh faces 24 charges over the elevated cobalt and caffeine levels returned by Midsummer Sun after his Gosford Cup win in January.
He has named Brennan, a partner in the Flemington Equine Clinic, as the person who supplied him with the substance "Vitamin Complex" later analysed and found to contain cobalt.