Override Set Expiration Date logic to push out the expiration date based on time of checkout

override-set-expiration-date-pmpro.php

<?php
/**
 * Manually overrides the YYYY-MM-DD settings of a set expiration date level.
 * If the checkout is 15-30 July of the current year, push it out by another year.
 * The example expiration date is 31 July of current year in the Set Expiration Date Add On.
 *
 * Tweak all the code accordingly for your needs, and add level ID checks for multiple level compatibility.
 * To add this code to your site you may follow this guide - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_override_sed_date( $date ) {
    global $pmpro_level;
    
    // Only run on the checkout page.
    if ( ! function_exists( 'pmpro_is_checkout' ) || ! pmpro_is_checkout() ) {
       return $date;
    }
    
    // Only if the checkout level has a set expiration date, change it.
    if ( ! empty( $pmpro_level ) && pmpro_getSetExpirationDate( $pmpro_level->id ) ) {
        $current_month = (int) date( 'n' );
        $current_day   = (int) date( 'j' );

        // If the checkout period is 15-30 July, set the expiration date to the following year.
        if ( $current_month === 7 && $current_day >= 15 && $current_day <= 30 ) {
            $date = 'Y2-07-31';
        }
    }

    return $date;
}
add_filter( 'pmprosed_expiration_date_raw', 'my_pmpro_override_sed_date', 10, 1 );