错误的日期保存

I have a form in which I have integrated calender field :

Publish date and Unpublish date

When I am sbmitting this form I have Publish date = 1/18/2017 and unpublish date = 1/19/2017;

In Controller i am making custom time

$pubdate =  strtotime("$publish_date 00:00:00");  
$unpdate =  strtotime("$publish_date 23:59:59");  

In db it's saving wrong date

select from_unixtime(publish_date) as a , from_unixtime(unpublish_date) as b from banner ;

output :

'2017-01-18 05:30:00.000000', '2017-01-20 05:29:00.000000'

where I'm doing wrong

Or is there any way to save the time :

Like publish date = 01/18/2017 (m/d/Y) it should become 01/18/2017 00:00:00 and save it in db like : 1551398401

output :

'2017-01-18 05:30:00.000000', '2017-01-20 05:29:00.000000'

object(DateTime)[2]
  public 'date' => string '2017-01-18 05:30:00.000000' (length=26)
  public 'timezone_type' => int 3
  public 'timezone' => string 'UTC' (length=3)

This is how it stores in database. To display this

<?php
echo date_format($dbdate, 'd/m/y H:i:s'); //Output: 01/18/2017 00:00:00
?>