How long should I have to brush my teeth?
If you follow proper brushing technique,ideally all surfaces of your teeth is cleaned in 2 minutes.
Its not that if I brush for more time, my teeth will become brighter.
Too much of anything is good for nothing.This applies for your brushing too.
Because prolonged brushing may erode your tooth enamel and you will land up in other problems like sensitivity, gum recession etc…