there is a filter you could use

$surcharges = apply_filters('wppizza_filter_surcharges', $surcharges, $session, $options, $module);

(you probably do not need the 4th parameter and perhaps not even the third)
so something like

add_filter('wppizza_filter_surcharges', 'my_surcharges', 10, 2);
function my_surcharges($surcharges, $session){
/* 
do your calculations based on time, and whats in the cart (i.e $session) 
and return appropriate surcharges 
*/
return $surcharges;
}