Combined Effect Lasers

ive saved some money and im having my teeth whitend by my dentist on friday.
He is using the laser treatment?,combined with custom made mouth trays which i have to use overnight.
To be honest,i m quite excited,ive gone years with discoloured teeth,.I m saving some money every month to pay for top ups.
Question is,,,what can i do to maintain the whiteness,and how long does the effect last,?,,thanks for your help