Trigger WP CRON from a date in a Custom Field?

You will have to write a plugin which creates a daily cron job in the WordPress system.

Here’s an article describing how to write a cron plugin:

https://wpguru.co.uk/2014/01/how-to-create-a-cron-job-in-wordpress-teach-your-plugin-to-do-something-automatically/

The function (callback) that you trigger in the cron plugin will use WP_QUERY to get a list of all your published custom post types after a certain date.

e.g.

$my_query = new WP_Query( array(
    'post_type' => 'your-cpt-name-here',
    'order' => 'ASC',
    'posts_per_page' => 1,
    'date_query' => array(
        array(
            'after' => '1 day',
        )
    ),
) );

Run through the results and send an email using wp_mail().

Alternatively, ask on fiver.com and get a developer to do it for you. It’s pretty simple so won’t cost very much at all.