Solved the date format problem, based on this post and this article
Changed the file: /components/com_jamegafilter/assets/js
_date = new Date(value.frontend_value[0]*1000);
_value = _date.getDate()+'-'+(_date.getMonth()+1)+'-'+_date.getFullYear();
TO
const monthNames = ["januari", "februari", "maart", "april", "mei", "juni", "juli", "augustus", "september", "oktober", "november", "december"];
const _date = new Date(value.frontend_value[0]*1000);
_value = _date.getDate()+' '+(monthNames[_date.getMonth()])+' '+_date.getFullYear();
Result the full date