Snippet to adjust Date Range Estimated delivery based on shipping method.PluginHive Plugins : https://www.pluginhive.com/plugins/

functions.php

/**
 * Snippet to adjust Date Range Estimated delivery based on shipping method.
 * Created at : 28 Nov 2018
 * Updated on : 04 Jan 2019
 * PluginHive Plugins : https://www.pluginhive.com/plugins/
 * Gist Link : https://gist.github.com/xadapter/983ecf750115b2c0471f55a35a57f8ef
 */

// Adjustment on Cart and Checkout page.
add_filter( 'xa_estimated_delivery_cart_checkout_page_html_formatted_date', 'xa_modify_cart_page_text', 10, 2 );
function xa_modify_cart_page_text( $text, $test ) {
	$shipping_method=WC()->session->get( 'chosen_shipping_methods' );
	if(!empty($shipping_method))
	{
		$shipping_method=strtolower($shipping_method[0]);
	}
	$display_text 	= "Estimated Delivery";		// Text for Estimated delivery
	$date_format 	= 'd/m/Y';					// Date Format

	$adjustment = array(
		'table_rate:2:1'	=> array(						// shipping method name
			'min'	=> '-2',						// Date Lower range
			'max'	=> 6,						// Date Higher range
		),
	);
	$text_array 	= explode( '<td data-title="'.$display_text.'">', $text );
	if(!isset($text_array[1])) // check text format is simple 
	{
		return $text;  
	}
	$text_array 	= explode( '</td></tr>', $text_array[1] );
	$prev_date_arr 	= explode( '-', $text_array[0] );				//Contains the date in case of date range

	if(!empty($shipping_method)  && isset($adjustment[$shipping_method]) && isset($prev_date_arr[1]) && !strpos($prev_date_arr[1], 'days') ) { 

		$lower_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[0]) );
		$higher_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[1]) );
		$min 				= $adjustment[$shipping_method]['min'];
		$max 				= $adjustment[$shipping_method]['max'];

		$lower_range_date->modify( "$min day" );
		$higher_range_date->modify( "$max day" );

		$text = '<tr class="shipping"><th> '.$display_text.'</th><td data-title="'.$display_text.'"> '.$lower_range_date->format($date_format) .' - '. $higher_range_date->format($date_format).'</td></tr>';
	}

	return $text;
}


// Adjustment on Thank you page.
add_filter( 'xa_estimated_delivery_thank_you_page_html_formatted_date', 'xa_modify_thankyou_page_text', 10, 2 );

function xa_modify_thankyou_page_text( $text, $test ) {

	$shipping_method=WC()->session->get( 'chosen_shipping_methods' );
	if(!empty($shipping_method))
	{
		$shipping_method=strtolower($shipping_method[0]);
	}
	$display_text 	= "Estimated Delivery";		// Text for Estimated delivery
	$date_format 	= 'd/m/Y';					// Date Format

	$adjustment = array(
		'table_rate:2:1'	=> array(						// shipping method name
			'min'	=> 5,						// Date Lower range
			'max'	=> 6,						// Date Higher range
		),
	);



	$prev_date_arr 	= explode( '-', $text );		// Date as array	

	if(!empty($shipping_method)  && isset($adjustment[$shipping_method]) && isset($prev_date_arr[1]) && !strpos($prev_date_arr[1], 'days') ) {

		$lower_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[0]) );
		$higher_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[1]) );
		$min 				= $adjustment[$shipping_method]['min'];
		$max 				= $adjustment[$shipping_method]['max'];

		$lower_range_date->modify( "$min day" );
		$higher_range_date->modify( "$max day" );

		$text 				= $lower_range_date->format($date_format).' - '.$higher_range_date->format($date_format);
	}

	return $text;
}

add_filter( 'woocommerce_package_rates', 'add_est_delivery_to_shipping_rates', 11, 2 );
function add_est_delivery_to_shipping_rates($shipping_rates, $package ) {
	$adjustment = array(
		'flat_rate:4'	=> array(						// shipping method name
			'min'	=> '-1',						// Date Lower range
			'max'	=> 6,						// Date Higher range
		),
		'free_shipping:5' => array(
			'min'	=>1,
			'max'	=>1),
	);
	$date_format 	= 'd/m/Y';					// Date Format
	foreach ($shipping_rates as $shipping_method => $shipping_rate_data) {
		$method_meta_data_arr = $shipping_rate_data->get_meta_data();
		if(array_key_exists($shipping_method, $adjustment) && isset($method_meta_data_arr['ph_est_delivery_date']))
		{
			$package_est_delivery=$method_meta_data_arr['ph_est_delivery_date'];
			$prev_date_arr=explode('-', $package_est_delivery);
			if(!isset($prev_date_arr[1]))
			{
				continue;
			}
			elseif(strpos($prev_date_arr[1], 'days'))
			{
				$lower_range_date=trim($prev_date_arr[0])+$adjustment[$shipping_method]['min'];
				$higher_range_date=trim(explode('days', $prev_date_arr[1])[0])+$adjustment[$shipping_method]['max'];
				$estimated_delivery_date=$lower_range_date.' - '.$higher_range_date.' days';
			}
			else
			{
				$lower_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[0]) );
				$higher_range_date 	= date_create_from_format( $date_format, trim($prev_date_arr[1]) );
				$min 				= $adjustment[$shipping_method]['min'];
				$max 				= $adjustment[$shipping_method]['max'];

				$lower_range_date->modify( "$min day" );
				$higher_range_date->modify( "$max day" );
				$estimated_delivery_date=$lower_range_date->format($date_format) .' - '. $higher_range_date->format($date_format);
			}
			$shipping_rate_data->add_meta_data( 'ph_est_delivery_date', $estimated_delivery_date );
		}
	}
    return $shipping_rates;
}