custom field value date convert to unix timestamp problems

Looking at http://www.php.net/manual/en/datetime.formats.date.php I dont think strtotime will convert a DD/MM/YYYY to time correctly.

However it can do MM/DD/YYYY or YYYY/MM/DD.

Try using the date format of YYYY/MM/DD

Or if thats not to your liking then you can use the same date format but you will have to, on save, split up the date and convert it to unix datestamp a diff way. You could use:

$date = "dd/mm/yyyy";
$date = explode("https://wordpress.stackexchange.com/", $date);
$date = mktime(0, 0, 0, (int)$date[1], (int)$date[0], (int)$date[2]);