It's surely too late for JamesBen08 but if you have v 1.7.8.x and take into account that 'date_format' produces a string then
{if ($smarty.now|date_format:'%Y-%m-%d %H:%M:%S' > '2022-12-15 00:00:00') && ($smarty.now|date_format:'%Y-%m-%d %H:%M:%S' < '2023-01-02 00:00:00')}
...
{/if}
will do in my template for christmas season.