I was told 4 minutes with the trays followed by nothing for half an hour. I do it just before bed so I'm not tempted to drink anything. But some months ago my dentist suggested that I might not need to do it every night but rather to brush with the stuff (I use Prevident) and do the trays once or twice a week. But my oncologist seemed to think I should keep up the trays. I'm following her advice, though once a week or so I might skip the trays and just brush with it.