php strtotime provide format code example

Example 1: php start of day epoch

$beginOfDay = strtotime("today", $timestamp);
$endOfDay   = strtotime("tomorrow", $beginOfDay) - 1;

Example 2: php date strtotime format

$date = '25/05/2010';
$date = str_replace('/', '-', $date);
echo date('Y-m-d', strtotime($date));