Depending on the type of flea product you intend to use, you will need to reapply the treatment from as early as a day to as late as a few months. Flea capsules usually have the shortest service life, and they usually need to be administered within 24-48 hours. Spot-on solutions usually need to be reapplied every 4 to 6 weeks.
Dog shampoos usually last for as little as a few days or a week, so you may need to couple these with another form of treatment. The same goes for flea pills. A dog collar provides the longest protection of up to 8 months.