It is dirty hack, but it should work, if you are sure that dates are in this AM/PM
format, you'll have to remove last 3 characters from the string (AM or PM plus space):
$myDateTime = DateTime::createFromFormat('jS F H:i', substr($datetest, 0, -3));
Fiddle here.
Also, remember that using AM/PM
is valid for up to 12 Hour, 20:00 AM/PM is INVALID format.