Add Listing Hooks

I would like to add a function into the Add Listing page that sets the post_title based on two custom fields. So rather than the user inputting the post title I would have a function that sets the post_title using something like this:
$my_post[‘post_title’] = esc_html($_POST[‘custom’][‘field1’] . $_POST[‘custom’][‘field2’]);

Does anyone know what hook/filter I can use? I have found these but there isn’t much documentation available on what each of them does:

hook_add_form_top()
hook_add_form_bottom()
hook_add_form_post_save_data($val)
hook_add_form_post_save_extra($postID)
hook_add_build_field($string)