To make a timestamp from a particular date...:
$time = "06/12/2013 6:41 pm";
$format = "%m/%d/%Y %l:%M %P";
$ts = strptime($time, $format);
$ts = mktime($ts['tm_hour'], $ts['tm_min'], $ts['tm_sec'], $ts['tm_mon'], $ts['tm_mday'], ($ts['tm_year'] + 1900));
after you can use like you want:
$mysql_timestamp = date("Y-m-d H:i:s", $ts);