Paint sealants are designed to last for many months. The manufacturer will indicate how long each particular product will last. However, if it is applied correctly, most paint sealants will last for a full twelve months. This means a lot less work for you! However, as a note of caution, you cannot apply paint sealer over wax. This is because bonds need to form between polymers on the surface your paint and the sealant. Wax or other oils get in the way. You can apply wax over the sealant if you wish. You also cannot apply paint sealer to new paintwork. You need to let it cure for around 30-90 days before you add the sealant. This is because the paint will continue to release solvents over this time and the sealant will trap them in and ruin the finish.