Add term meta to WordPress terms when created

functions.php

<?php

//replace my_taxonomy with your own taxonomy slug

//The hook create_{$taxonomy} is fired when terms are created in $taxonomy
function my_taxonomy_meta_add($term_id, $tax_term_id){
    //here you can add whatever meta you need
    add_term_meta($term_id,'_date_created',time());
}
add_action('create_my_taxonomy','my_taxonomy_meta_add',10,3); 

//optionally display the custom meta on the term edit form (mine is not editable)
function my_taxonomy_edit_form($term, $tax){
    $created = get_term_meta($term->term_id,'_date_created',true);
    if(!empty($created)){
        $dt = new DateTime();
        $dt->setTimeStamp($created);
        $dt->setTimezone(new DateTimeZone('Pacific/Auckland')); //use your own time zone

        echo '<tr class="form-field date-created-wrap">
			<th scope="row"><label>Date created</label></th>
			<td>' . $dt->format('d F Y H:ia') . '</td>
		</tr>';
    }
}
add_action('my_taxonomy_edit_form_fields', 'my_taxonomy_edit_form',10,2);