Prism starts counting clear days from the following day the treatment is completed.  This ensures that your horse can safely race or trial.   So if you give the horse a treatment on the 1st and it has a clear day buffer of 3 days, Prism counts the 2nd, 3rd and 4th as clear days and the horse is able to race or trial on the 5th.

Please note this is a guide only and you are responsible for presenting your horse clear on Race Day.