Hi,
Your PHP and your Joomla are not right configured for the time shift.
When the plugin convert the date "18/06/2014 00:00:00" into an unix timestamp, I got the date "17/06/2014 23:00:00".
It means that you have a different timezone between your PHP and your Joomla.
I can add a new option in the datepicker so it can be independent for the timezone and add (or remove) the number of hours to get the right date but I do not have access to your admin panel to configure the plugin.
So I have hardcoded the timezone shift into the plugin so now the dates are correct.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.