Magento 1 - How to check if a product is new

You absolutely must NOT convert and validate dates manually, because this can cause timezone issues. Magento has built-in method isStoreDateInInterval() in Mage_Core_Model_Locale class. So you should create helper method which can look like this

function isProductNew(Mage_Catalog_Model_Product $product)
{
    $newsFromDate = $product->getNewsFromDate();
    $newsToDate   = $product->getNewsToDate();
    if (!$newsFromDate && !$newsToDate) {
        return false;
    }
    return Mage::app()->getLocale()
            ->isStoreDateInInterval($product->getStoreId(), $newsFromDate, $newsToDate);
}

More details you can find here http://quicktips.ru/all/check-product-is-new/

There's no single method call. At least I'm not aware of it.

Nevertheless you can always use something like this:

<?php if (date("Y-m-d") >= substr($_product->getNewsFromDate(), 0, 10) && date("Y-m-d") <= substr($_product->getNewsToDate(), 0, 10)) : ?>
...
<?php endif ?>

Sorry I'm not good in PHP date comparison.

Good question by the way.

For reference, here's the helper method that I came up with to check for newness. It supports both the Featured dropdown as well as the dates, and supports either date being empty as well.

public function isNew($product)
{
    if ($product->getData('featured_product')) {
        return true;
    }

    if ($product->getData('news_from_date') == null && $product->getData('news_to_date') == null) {
        return false;
    }

    if ($product->getData('news_from_date') !== null) {
        if (date('Y-m-d', strtotime($product->getData('news_from_date'))) > date('Y-m-d', time())) {
            return false;
        }
    }

    if ($product->getData('news_to_date') !== null) {
        if (date('Y-m-d', strtotime($product->getData('news_to_date'))) < date('Y-m-d', time())) {
            return false;
        }
    }

    return true;
}

UPDATE: Thanks to @Rooooomine for mentioning that this manual date conversion I suggested is a very bad idea due to potential locale issues. Check out Mage::app()->getLocale()->isStoreDateInInterval($product->getStoreId(), $newsFromDate, $newsToDate) instead.