Change user role of a particular user at specific time

You can do something like this

add_action("after_switch_theme", "schedule_cron_job"); // hook the schedule on theme switch or plugin activation based on the your usage also switch your theme after putting this on functions.php
function schedule_cron_job(){

    if (! wp_next_scheduled ( 'import_into_db' )) {

        wp_schedule_event(strtotime('12:04:00'), 'daily', 'import_into_db');

    }

}

add_action('import_into_db', 'your_cron_job'); // You were hooking to wp


function your_cron_job(){

    $u = new WP_User(3);
    $u->set_role('editor');

}

You can use cron manager plugins to check if cron job is scheduled or not.