差异两个日期时间在PHP问题中使用diff函数？

I want to get date time difference between two date time. In my application i am running a counter for 06:00 PM (18:00:00) everyday when user open application they will appear a counter. when i see application in morning Like in 11 AM time difference will appear around 16-17 hrs but should be appear 7 hrs.

Code what i have done :

date_default_timezone_set("Asia/Kolkata");
$date = date('Y-m-d');
$currentDate = date('Y-m-d h:i:s');
$redeemDate = $sql->row()->lottery_date . " 18:00:00";

$datetime1 = new DateTime($currentDate);
$datetime2 = new DateTime($redeemDate);
$interval = $datetime1->diff($datetime2);

From my code when i see in AM time interval is not appear properly.

Any clues?