How long between professional whitening and using crest strips?

Different professional whitening treatments can affect your teeth and gums in unique ways, so contacting the dentist where you received the treatment will be your best solution, as specific details about your whitening treatment might influence this timeline.
Based on your results, they may even recommend a different whitening treatment going forward. I've also seen many patients who have whitening-resistant enamel and ultimately opted for cosmetic treatment for that long-lasting whitening result (i.e porcelain veneers, crowns, or bonding).