Objections to the participation of a horse entered in any race shall be made to the stewards and confirmed in writing by the objector. An objection to a horse entered in a race shall be made not later than one hour before the scheduled post time of the race in which such horse is entered, except that the stewards upon their own motion may consider an objection until such time as the horse becomes a starter.
Cal. Code Regs. Tit. 4, § 1751