how can I put particular action as I select any row of UIPickerView?

I am writing code like

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {    int n=row+1;    if(row == 0)        return [NSString stringWithFormat:@"%d minute", n];    return [NSString stringWithFormat:@"%d minutes", n];}

now I want to start timer as I choose any row, like row 5 has 5 mints, so I want to start timer with 5 mints, so what should I do, How can I choose particular row and press button and timer starts for that event?