Your dentist can provide you with a custom-made tray for at-home whitening. In this case, the dentist will give you instructions on how to place the bleaching solution in the tray and for what length of time. This may be a preferred option if you feel more comfortable whitening in your own home at a slower pace, but still with the guidance of a dentist. Out-of-office bleaching can take anywhere from a few days to a few weeks.