Using this tip we can record unit time for a student in a custom post meta field. 
We're going to use the action hook : wplms_before_every_unit for this purpose.

Add following code in WPLMS Customizer plugin -> customizer_class.php file:

1. Go to WP Admin -> Plugins -> editor -> wplms customizer -> customizer_class.php
2. Add following line of code in _construct file:

PHP Code:

 

add_action('wplms_before_every_unit',array($this,'track_unit_start_time'),10,1);

 

3. Add this function in class :

PHP Code:

 

function track_unit_start_time($unit_id){
 if(is_user_logged_in()){
   $user_id = get_current_user_id();
   $key = 'unit_start_time'.$unit_id;
   $check_exists = get_user_meta($user_id, $key,true);
   if(!isset($check_exists) || !is_numeric($check_exists))
    add_user_meta($user_id,$key,time());
 }
}

 


Above code records the timestamp when the user "First" views a unit.