Woocommerce Subscription : get length in day for a subscription product

Question

I am interested in showing my users how much % they save when purchasing a particular variation product.

For example if I have a variable subscription, with two variations.

1. £24 for 1 Week
2. £30 for 2 Week

Then save percentage = ( ((24 * 2) - 30) / 30 ) * 100 = 60%

I want to show Subscribe & save 60% when a user has selected product 2.

My progress

I know how to show this text on variation but I have problem fetching this percentage value.

Find my code below which is trying to get discount.

function add_data_point_for_savings($available_variations)
{
    if (is_array($available_variations)) {
        $product = wc_get_product($available_variations['variation_id']);
        $period = \WC_Subscriptions_Product::get_length($product);
        $parent_id = $product->get_parent_id();
        $parent_product = wc_get_product($parent_id);
        $minimum_price = $parent_product->get_variation_price('min', true);
        if (isset($available_variations['variation_id'])) {
            $available_variations['underline_text'] = 'Subscribe & Save 00%';
        }
    }
    return $available_variations;
}

add_action('woocommerce_available_variation', 'add_data_point_for_savings', 5);

As you can see I am adding this as a datapoint in available_variation.

I am stuck at getting day value for every variation. If I get day count for every variation I will be able to find the save percentage.

---

I am aware of these two functions.

1. WC_Subscriptions_Product::get_length Gives length eg. 6
2. WC_Subscriptions_Product::get_period Gives period eg. week, month

The issue with these functions is that it returns 0 when I try to get length.

To sum it all up.
I want to find the day count for a subscription product variation, given I have its id.