Limit WooCommerce coupon code to specific day of the week

Here is a complete solution with two hook features that restrict coupon usage to specific days of the week and display a custom error notification if the coupon is invalid.

1) Checking the validity of "certain days":

add_filter( 'woocommerce_coupon_is_valid', 'coupon_week_days_check', 10, 2);
function coupon_week_days_check( $valid, $coupon ) {

    // Set HERE your coupon slug   <===  <===  <===  <===  <===  <===  <===  <===  <===  <===  
    $coupon_code_wd = 'xyz';
    // Set HERE your defined invalid days (others: 'Mon', 'Tue', 'Wed' and 'Thu')  <===  <===
    $invalid_days = array('Fri', 'Sat', 'Sun');

    $now_day = date ( 'D' ); // Now day in short format

    // WooCommerce version compatibility
    if ( version_compare( WC_VERSION, '3.0', '<' ) ) {
        $coupon_code = strtolower($coupon->code); // Older than 3.0
    } else {
        $coupon_code = strtolower($coupon->get_code()); // 3.0+
    }

    // When 'xyz' is set and if is not a week day we remove coupon and we display a notice
    if( $coupon_code_wd == $coupon_code && in_array($now_day, $invalid_days) ){
        // if not a week day
        $valid = false;
    }
    return $valid;
}

      

        
        
        
      

    

2) Display custom error message for "certain days" coupon if invalid:

add_filter('woocommerce_coupon_error', 'coupon_week_days_error_message', 10, 3);
function coupon_week_days_error_message( $err, $err_code, $coupon ) {

    // Set HERE your coupon slug   <===  <===  <===  <===  <===  <===  <===  <===  <===  <===  
    $coupon_code_wd = 'xyz';
    // Set HERE your defined invalid days (others: 'Mon', 'Tue', 'Wed' and 'Thu')  <===  <===
    $invalid_days = array('Fri', 'Sat', 'Sun');

    $now_day = date ( 'D' ); // Now day in short format

    // WooCommerce version compatibility
    if ( version_compare( WC_VERSION, '3.0', '<' ) ) {
        $coupon_code = strtolower($coupon->code); // Older than 3.0
    } else {
        $coupon_code = strtolower($coupon->get_code()); // 3.0+
    }

    if( $coupon_code_wd == $coupon_code && intval($err_code) === WC_COUPON::E_WC_COUPON_INVALID_FILTERED && in_array($now_day, $invalid_days) ) {
        $err = __( "Coupon $coupon_code_wd only works on weekdays and has been removed", "woocommerce" );
    }
    return $err;
}

      

        
        
        
      

    

The code goes in the function.php file of your active child theme (or theme), as well as any plugin file.

This working code is tested on WooCommerce 2.6.x and 3.0+ versions.