$starttime   = 1362585600; //3.7凌晨
$nowtime   = 1362618921;//3.7早上
$off = ceil(($starttime - $nowtime)/86400); //倒计时
if ($off < 0) {
  $off = 0;
}
$b = $starttime - $nowtime;
$c = $b/86400;
$d = ceil($c);
var_dump(array('start-now'=>$b), array('float_day'=>$c), array('int_day'=>$d), array('off'=>$off));
if (-0 < 0) {
  echo '-0 < 0';
} else {
  echo '-0 > 0';
}

array
 'start-now' => int -33321
array
 'float_day' => float -0.385659722222
array
 'int_day' => float -0
array
 'off' => float -0
-0 > 0

$starttime   = 1362585600; //3.7凌晨
$nowtime   = 1362618921;//3.7早上
if (($starttime - $nowtime) < 0) {
  $off = 0;
} else {
  $off = ceil(($starttime - $nowtime)/86400);
}