[php] Subtract 1 day with PHP

Not sure why your current code isn't working but if you don't specifically need a date object this will work:

$first_date = strtotime($date_raw);
$second_date = strtotime('-1 day', $first_date);

print 'First Date ' . date('Y-m-d', $first_date);
print 'Next Date ' . date('Y-m-d', $second_date);