Set future date on a pending post

<?php
// http://www.gravityhelp.com/forums/topic/form-date-field-publish-date#post-71477
// the 10 (priority), 2 (arguments) is documented here http://codex.wordpress.org/Function_Reference/add_filter
// change the 64 here to your form ID
add_action('gform_after_submission_64', 'set_schedule_date', 10, 2);
function set_schedule_date($entry, $form){

        // get the post
        $post = get_post($entry['post_id']);

        // see note here http://codex.wordpress.org/Function_Reference/wp_update_post#Scheduling_posts
        $post->edit_date = true;

        // make sure it really is pending
        $post->status = 'pending';

        // change post schedule date in format [Y-m-d H:i:s] based on input from the entry
        // be sure to change the 18 here to your date input field
        $post->post_date = date('Y-m-d H:i:s', strtotime($entry['18']));

        // update the post
        wp_update_post($post);
}