Hello alexintras,
I had a similar issue with a client. I was able to fix it by modifying the plugin file of datefiledpicker_class.php, specifically the getTimestamp function. In there, it is only getting the Year, Month, and Day to get the timestamp which is used by get date. I added ".' 12:00:00'" to the end of the value set line so now my getTimestamp function looks like this below. Best I can figure out by tracking the code is that the timezone offset is causing the problem and by setting the time to like noon fixes it. I may be wrong but that is what worked for our client.
Hope this helps.
Regards,
Donald
private function getTimestamp($value) {
if(is_array($value)) {
$value = $value['y'] . '/' . $value['m'] . '/' . $value['d'].' 12:00:00';
}
$ret = hikashop_getTime($value);
return $ret;
}